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Dead Milwaukee Battery, might not be so dead afterall…

Several years ago, I bought a set of Milwaukee power tools. I love the tools, but one of the batteries seemed to die after a few years (but very little usage.) The batteries are like $80 and since I don't use the tools very often, I've never bothered replacing the one that seemed to be dead (since I have 2 batteries.)

However, today I came across a very cool tip.

Apparently these "dead" batteries are a known issue with Milwaukee and often the batteries aren't dead, but just need to be jump started. To awaken one of these dead batteries, place a standard 9-volt battery against the leads on your dead Milwuakee battery for 30 seconds (single lead on your Milwaukee is positive, the double lead is negative.)

Sure enough after doing this little tip, I was able to plug my battery in to the charger and it started charging it!


  • i have a lith ion 18v, when its charging the battery flashes red, while the charger is a constant red, it even turns green saying its fully charged. Im wondering if this is my issue since i didnt use the batteries in like 3 weeks. let me know what you think. Thanks a lot
  • @Cam:

    You can try it, it won't hurt anything. In my case the light just stayed a constant red, but it would never charge. I don't use the batteries a lot, so this happened after not using the battery in a few months (and then because I thought it was dead, I went a couple of years before trying this tip.)

    Doing this shouldn't harm the battery at all--there's not enough juice coming out to hurt the battery, but it appears there's enough to reset the battery's memory.
  • Wow- thank you for this. Both of my Milwaukee 18v batteries where dead. (I thought)
    They are both charged and running great. You just saved me at least $100.
    Thanks again-
  • That is awesome! My battery is working again.
  • We lol this work on the V28 battery?
  • My Lithium-ion 18v batteries (2) have five slots that fit into the charger.
    I have the same propblem that Cam has with the charger showing red then
    green but no power in the batteries. Which slots do I use to jump with the
    9 volt?
  • Hi,

    I'm having the same problem with two identical batteries that came with my Milwaukee drill. They're 18-volt batteries and I'm examining them in hopes of performing this trick you're recommending. However, would it be possible for you to post a photo of your battery? Mine has no exposed metal "leads," or anything that would resemble something to which you could simply hold a 9-volt battery. My battery connects to the charger by sliding into a series of 5 plastic grooves. Any metal contact points are within the battery itself.
  • I had the same problem with two "Red lithium" 18v batteries: charger pretends to charge, turns green after a while indicating a full charge but batteries are still dead. The solution? New charger from Amazon for less than 30 bucks. Both batteries work flawlessly and I'm glad I don't have to go through the pain of warranty replacement, yet.
  • Hi
    same story with the battery and the five grooves.
    Just where do you place the 9 volt battery?
    Anyone there
  • Both my 3.0Ah batteries seemed to have packed in around the same time. I was using them outdoors in very cold damp weather. The charger was flashing between red and green which indicates broken battery. So I took them home and forgot about them for a fortnight or so then thought I would give them another try. They are not that old or used and both have now charged up fine. Anyone else had a similar problem with cold damp weather ?
  • Rubbish, no leads on Milwaukee batteries, they slot into the charger this is not possible
  • This will help you identify the leads on your 5-connector battery:

    It is basically the outer two slots. The one with the white sleeve on it is the ground. You can look at the video to understand the proper orientation. Or you can just unscrew the top and identify it by its sleeve.

    I plan to try it on mine, once I dig up a 9V battery. But I have no specific knowldge on whether this will work.
  • Hopefully some of you are still following this thread and can maybe help a guy out here: I've had a Milwaukee cordless drill for about 3 years. I use it daily. It stopped working properly, so I purchased a refurbished one (similar to my first one). The batteries from my first one still work fine, but when I have them fully charged and put them on my new gun, nothing happens. BUT! (this is where I get lost...) If I put the batteries on the old gun and pull the trigger one time (this causes the LED light to come on on the old gun, but nothing else happens) and immediately put the battery on the new gun, it will work perfectly fine AS LONG AS I don't let the gun sit without being used for more than 3-5 minutes. My batteries work perfectly on a Milwaukee drill that my friend brought to the shop, so I don't believe it is a battery issue. Any help with what may be wrong with my refurbished gun? Thanks in advance!
  • Just got a brand new M18 3/8 one key impact driver... one battery started blinking green and red as soon as I put it in charger.... and it's BRAND NEW!
     Tried to call Milwaukee... busy, ( it's Friday night so, I figure I'll try on Monday.
    The more I thought about it, the more it bugged me... googled dead M18 battery, found this blog, and thought, why not?.... came into work, found a brand new 9 volt battery, jumped it to my 5ah M18...( let it go to about 7 volts)... snapped it in the charger and WA-LA!!!!..... works fine, charged fine!!
    Thanks VERY much, saved me the hassle of trying to return and deal with that!!
  • I just tried this on my m18 red lithium battery. It works, I did a bunch of google image search to find which leads are (+) and which were (-). I used a 12v psu and charged it for 40sec and then put it back on the charger. Next morning it showed all greed (4 bars) on the battery itself. Thank you!
  • Hate to say this but it worked, at first my 18 lithium battery did not work so I tried it again and left my 9 volt attached for a little longer then 30 seconds when I heard a sound like a pop so I disconnected it from the 9 volt and placed on my charger and to my surprise it worked I was happy as hell
  • Just tried it on my 18v and I will say after about 15seconds I heard the battery click. Held the 9 volt connected to it just a little longer and YES it does work.
  • Works like a charm! If you can follow these bloody easy directions, to figure out where the leads on the battery are, you bloody well shouldn't be using an 18v Milwaukee drill gun mate!
  • Yep, worked straight away - all good.
  • I pushed a new 9 Volt battery into dead Milwaukee battery as described above then placed it in the charger... and it worked!!!!...Thank you for the great tip!!!
  • Wow, I'm a bit amazed and a lot relieved. Bought a Milwaukee 18V drill at HD last year on sale for $100 when my ancient (8+ years) Ridgid drill finally stopped working at all (batteries both dead, bearings and gears getting kinda shot) and the Milwaukee worked well enough. But for the past few months the charge it holds has dropped steadily. I charge maybe 2 or 3 times per week, about half the time when I've run it down to zero, the other half when it's just showing 1 LED when the button is pressed.

    Yesterday it stopped utterly. Putting the battery into the charger resulted in about 3 seconds of red, then glowing green as though fully charged. Weird, as it had been able to run for about 2 minutes before that, the battery obviously not totally dead. I tried pressing and holding the button for a lot of seconds on impulse, and presto, the LEDs went through some sort of 'diagnostic' series of blinks... but nothing changed, still wouldn't charge, still told me it was fully charged when plugged in while flashing 1 LED with a single button push.

    So this morning I searched... and found this great thread. Tried it with a nearly dead 9V battery (showing under 8V with a multi-meter before trying this) and held a couple of pieces of 1/8" aluminum wire with the ends squashed flat to squeeze into the outer two battery slots. Wore safety goggles, held battery with pliers, kept fire extinguisher at hand... but nothing bad happened. Didn't look like anything happened. Certainly no *POP* sound as one user reported here. I left it connected for about 1 minute. Checking the 9V it was slightly warm. Okay, so something happened. Put the Milwaukee M18 battery into its charger, and WOW, it lit up RED! Stayed that way for about 10 minutes, then went to green. Testing in the drill it works now, which is amazing, as I have a bunch of work to get done today and some of it requires a hand drill.

    So it seems the battery needs a jump start eventually. If it dies again I'll try again. Oh yeah, and the 9V meters at 0 volts now. Just the slightest jump of the needle when connecting. So it plainly dumped whatever it had into the drill battery.
  • Too good to be true as it turns out. I should have waited a day or two before gleefully reporting success. While the jump-start with the 9V battery did give the battery the ability to take a charge, after a few uses totalling around 2 minutes of drill time it died again and now refuses to take a charge. I'll have to go get some cheap 9V batteries and see if this is to be a regular thing until I feel like coughing up $100 plus tax for a new battery.
  • Worked for me too! I just paralled a fully charged v18 L-Ion battery with my v28 L-Ion battery that wouldn't charge (Charger flashing Red-Green). I let it "cook" for about 15 minutes, put the v28 on the charger and viola! Solid red LED on charger and first red battery LED charge indicator is lit.
    OK. I'll share a Ni-Cad trick with you guys. If you have one that wont charge or only partly charges, do the same as above, but double the voltage. For example, put (2) 18 volt batteries in series to restore one 18v battery. just connect it for only about 10 to 15 seconds. What this does is it burns off the sulfates that are shorting the battery out internally. This works most of the time. Repeat if it doesn't.
  • Hi
    Just want to know would this trick work with any lipo batteries as I have a few dead RC drone batteries that are dead.
  • Yes it works great had a "RED LITHIUM" M18 5.0 that was left on my impact and not charged for about 5month. Placed the battery on my charger and received a flashing red-green-red-green. Indicating a damaged battery. Jumped the power and ground with a 9v. placed the 5.0 on the charger and it showed the charging light and the battery changed completely
  • I tried. I got the green light on the charger but the battery continues dead. Huh?!?!?! I will let it sit and see what happpens. Then I will try the 9volt thing again.
  • Have two of the 48-11-1828 XC one works fine, the other will not work in my tools. Well it will if I only charge it 3/4 to just when the forth LED on the battery turns on. If charged longer the green light on the charger will not come on indicating a full charge and the battery will not work in the tools. I first ran onto this over two years ago and just let the battery sit. The LED lights on the battery would come on by themselves and stay on for maybe a day or two... weird. After sitting for over two years I grabbed the battery and put it on the charger. I could hear the charger cycle , tick..tick..tick and the first LED on the battery would blink in time with the ticking from the charger. After about three minutes the first LED stop flashing and stayed on all the time. I knew the battery was taking a charge. after the second LED on the battery came on I pulled the battery, put it in one of my tools and "voila" it powered the tool. I put it back into the charger and fifteen minutes later with 4 LED on I tested in the tool -No Go

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Milwaukee M18 Cordless Power Tool Battery Sizes Explained

Milwaukee M18 Battery Pack Lineup

Yesterday, we posted about two new Milwaukee M18 batteries that are coming soon – CP3.0 and XC8.0.

To start things off, you should know that all Milwaukee M18 batteries are designed to work with any Milwaukee M18 tool. There are some physical compatibility issues with a couple of earlier tools, but in those cases, Milwaukee will update those products for free.

Milwaukee M18 Battery Sizes

Milwaukee M18 Compact vs XC vs High Demand Battery Size

There are 3 main M18 battery size categories: CP, XC, and HD.

CP battery packs are the compact batteries, with 5 Li-ion cells. The CP labeling is fairly new, and should help to make things clearer.

XC battery packs are the “extended capacity” battery packs, with 10 Li-ion cells. Unless changes were made, M18 XC batteries will give certain tools a slight power boost. For instance, the “XC effect” should give M18 drills a roughly 10%  increase in power.

HD battery packs are High Demand batteries, built with 15 Li-ion cells. These batteries deliver the longest runtime, and run cooler, keeping up with the heaviest duty Milwaukee M18 cordless power tools.

Milwaukee M18 High Output

Milwaukee announced new M18 High Output batteries in 2018, and has expanded the selection with the addition of a new High Output compact battery, and a higher capacity XC battery.

The “standard” batteries are built with 18650 cells, whereas the new High Output batteries are built with larger 21700 cells. The 21700 Li-ion battery cells are available at higher charge capacities, delivering longer runtime. Not only that, the cells can provided more power, and Milwaukee’s High Output battery packs run cooler.

Thus, the M18 High Output batteries can literally deliver higher output than the “standard” batteries.

An overly simplified way of thinking about it is that a Milwaukee High Output battery bumps you up to the next level of runtime, but in a smaller size battery pack.

The new CP3.0 battery provides higher capacity than the existing CP2.0 battery, and is said to have “XC power” but in a more compact size. The newest XC8.0 battery provides nearly the same charge capacity as the HD9.0 battery.

What do the Numbers Mean?

We have an entire article devoted to charge capacity, here.

The numbers following the size designation is the charge capacity. A CP3.0 battery has a 3.0Ah charge capacity; an XC5.0 battery has a 5.0Ah charge capacity; an HD12.0 battery has a 12.0Ah charge capacity.

An Ah is an amp-hour, and can tell you how much runtime a battery will provide, relative to battery packs of other sizes.

Which to Choose?

Generally, you could or should choose the size of battery that is appropriate for the tool. If you’re not sure, check out the contents of that tool’s kit options, if available. A compact drill or impact driver might be best matched up with a compact battery, while a circular saw will likely be better paired with an XC or even HD battery.

Larger battery packs, in an XC or HD battery compared to a CP battery sense, are capable of delivering more power, and run cooler, which can affect runtime and longevity. Of course, they also deliver longer runtime. The High Output batteries cloud things up a little, since they can deliver more power than standard-size batteries of the same CP, XC, or HD size families.

Related: Milwaukee M12 CP3.0 vs XC3.0 Battery Differences

What’s most important to you?

Do you want longer runtime? Select a battery with a higher charge capacity.

Do you want the most for your money? Crunch some numbers and select the battery pack with the lowest price-per-amp-hour ratio, or highest amp-hour-per-dollar ratio. Sometimes the best pricing can be found by buying a 2-pack.

Some users might prefer to buy one XC8.0 battery, while others might instead prefer two XC4.0 batteries. But if you’re running high powered tools, an HD12.0 battery could very well last longer than three XC4.0 batteries.

Also, keep in mind that higher capacity batteries take longer to recharge, and multiple batteries can require greater attention if you have more batteries to charge than you have chargers.

Although the High Output batteries offer higher capacities and can deliver more power than batteries from the same CP/XC/HD class, but they’re also physically larger, and also heavier.

Current Availability

CP3.0 and XC8.0 batteries are coming soon. All the others on the list are presently available.

Compact (CP)

  • 1.5Ah
  • 2.0Ah
  • 3.0Ah – High Output

Extended Capacity (XC)

  • 3.0Ah
  • 4.0Ah
  • 5.0Ah
  • 6.0Ah – High Output
  • 8.0Ah – High Output

High Demand (HD)

  • 9.0Ah
  • 12.0Ah  – High Output


Hopefully this clears things up. I’d be glad to help if you could use additional clarifications.

Which battery sizes do you typically use? If not with Milwaukee M18 tools, then with your brand of choice?

Sections: Cordless, EditorialTags: Milwaukee M18More from: Milwaukee

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When Milwaukee originally announced RedLithium batteries back in 2010, they replaced the original line of M12 and M18 lithium-ion packs. Not content to simply accept a fancy name without understanding the technology behind it, we began our research. In a nutshell, Milwaukee RedLithium battery technology combines advanced electronics and temperature resilience and control to generate reliable, consistent power.

To get the best information possible, we spoke with Paul Fry. He serves as senior vice president of product management at Milwaukee Electric Tool company. Paul has been working with Milwaukee RedLithium technology since the start. If we really wanted to understand what made RedLithium batteries special, Paul could help.

Milwaukee RedLithium Battery Technology In the Beginning…

So, back at the dawn of lithium-ion, Milwaukee Tool actually brought in some folks from MIT. They wanted to get into the business of building actual battery cells. Seriously, they were working with actual battery cells to adapt them for use with cordless power tools. This is actually pretty insane because it meant that Milwaukee owned battery production equipment at one point. They also hold more than a few lithium-ion battery patents.

This is highly unusual, to say the least. Before lithium-ion hit the scene, the entire industry purchased their Ni-Cd cells from one of two places. For the most part, they let the manufacturers also build the battery packs. This led to less-than-stellar solutions that couldn’t take much abuse.

Still…for NiCad, it worked…most of the time.

Milwaukee RedLithium Battery Technology

How Lithium-ion Batteries Differ from NiCd and NiMH

NiCd and NiMH battery packs don’t take much to make. You have no electronics. The packs require no significant temperature monitoring. Recharging doesn’t take much intelligence either.

Lithium-ion battery technology changed all of that overnight. Batteries suddenly got “smart”.

When Milwaukee moved to lithium-ion as a platform, they had to change the way batteries were traditionally made. Back then, only a couple of battery manufacturers existed on the market to figure out these challenges. Now there are around 7 mainstream companies:

  • Tesla – while they work closely with Panasonic, the Gigafactory is the world’s largest lithium-ion manufacturing plant in the world. It’s also based in the USA.
  • Panasonic – located in Japan, the United States, and China
  • LG – has Li-ion manufacturing facilities in Poland, the USA, Soiuth Korea, and China
  • Samsung SDI – manufactures Li-ion cells and packs in South Korea, China and Hungary
  • CATL – Chinese manufacturer of Lithium-ion batteries
  • BYD – Both a brand and battery manufacturer with plants in China and Brazil
  • Grepow – Making mostly consumer electronics batteries for R/C devices, drones, and other items, Grepow is based in China.

Increased Pack Complexity

On top of the growing number of manufacturers, the complexity of battery packs also increased. Because Li-ion required manufacturers to shift their focus to building better packs, it took the pressure off having to develop actual cells. Now, cell manufacturing gets handled by a few key manufacturers who do a pretty good job.

18650 lithium-ion cells

Like many of the top tool manufacturers, Milwaukee designs its own actual battery packs. Having started early, they just have more experience with lithium-ion than most. Milwaukee Tool theorizes that you can take the best battery cell in the world, but without great electronics and protection, the resulting pack performs poorly.

Check our article on All Milwaukee M18 batteries compared

Leveraging Technology and Talent

Milwaukee Tool quickly transitioned from trying to build battery cells to realizing they could retain these battery-geniuses on staff. They quickly redirected their efforts towards driving the partner manufacturers to maintain the best cell construction. Simultaneously, they adapted the technology and characteristics of the battery packs to meet user expectations.

These teams continued to control the production of the battery pack itself and also focus specifically on the development of the tool, pack, and charger electronics. The original lithium-ion battery packs had some electronics. Eventually, Milwaukee deployed additional electronics to monitor and implement new circuits. These analyzed the signals between the batteries and the tools and from the batteries to the chargers.

RedLithium technology was starting to take shape.

According to Milwaukee Tool, there ends up being three major places to focus when considering battery technology:

  1. Battery pack construction
  2. The actual lithium-ion cells within the pack
  3. The electronics within the battery pack (and consequently, the electronics within the tool and the charger)

Smart Milwaukee RedLithium Batteries

The transition from “dumb” batteries to “smart” batteries coincided with the advent of lithium-ion cells. Batteries went from virtually no electronics to systems that monitored all aspects of a battery pack’s charging and discharging functions. For example, during charging, the battery pack must speak to the charger, or overcharging can happen.

What’s an overcharge? If the battery charges beyond its capacity, the cell will break down and cease to work (or worse). Conversely, you could also take a battery pack over its temperature limits during the use of the tool. That can happen when the current draw exceeds limitations. That can melt your motor and let out the “magic smoke”. It can also damage the battery at the same time.

To avoid this, near-constant communication is happening during charging and discharging. The system monitors and adjusts the cells as well as the motor for optimum use and safety.

Editor’s note: Overcharging is when the battery pack is overloaded from the charger (power INTO the battery). Overload is when the tool is being used (power OUT FROM the battery) and the current draw goes up too high (for example, when the bit is too large or the torque too consistently high). In these cases, a well-designed tool turns itself off to protect both the tool and battery. A good battery-tool system monitors both aspects of this energy usage.

How Milwaukee RedLithium Technology Increased Runtime

The other side of the equation deals with run-time. With the advent of lithium-ion batteries, Milwaukee began providing discharge protection on the battery pack itself. This eliminated the need to discharge the battery fully by holding down the trigger, etc.

For anyone who has used NiCd or even NiMH, you are familiar with the memory effect and the tendency for the battery to lose its potential to hold a charge over time. Running it out was a frequent and popular method of regaining the battery’s maximum potential (or at least as much as possible). What users were really doing was “crashing the voltage” of the pack. Eventually, this hurt the battery.

Electronics stop the tool from discharging the battery to the maximum amount. This protects it from losing the ability to charge fully and completely. When a Milwaukee tool stops, it actually has a little charge left in the battery. The electronics step in to say “It’s time to charge the tool, quit working—you’re done.”

battery pack cells skeleton view

Thermal Protection in Milwaukee RedLithium Battery Technology

Thermal protection provides an equally important feature for the electronics that go into lithium-ion battery packs. This plays a role when cutting a bunch of lumber or any application using high amounts of torque or “trigger time”. In use-cases like this, you could easily take the pack up above its temperature threshold.

Milwaukee RedLithium electronics cut off the pack when a too-high threshold gets reached. What we find interesting is the observation that Milwaukee’s original lithium-ion batteries also contained electronic overload and thermal protection. Those early batteries simply cut out a lot earlier than newer RedLithium models. Runtime and torque capabilities took another leap with the advent of RedLithium High-Output batteries.

According to Paul, the electronics didn’t change all that much.

Advancements in cell technology, however, went through the roof.

Cell Construction and Chemistry Work Together

The newest Milwaukee RedLithium battery packs simply keep the overall battery cooler thanks to a change in cell construction and chemistry. The new potential and capability for increased load from the cells allowed the electronics to adjust, recognize this, and respond accordingly.

Remember those numbers above? That’s where all this increase came from. It’s real, not just marketing or a different way of measuring performance. The new RedLithium batteries literally build up heat slower and thus run longer before protection kicks in.

  • Milwaukee RedLithium Battery Technology - thermal protection
  • Milwaukee Redlithium High Output pack internals

Here’s how RedLithium differs in terms of performance, from its predecessors (these are “up-to” numbers):

  • 40% More Run-Time
  • 20% More Speed
  • 20% More Torque
  • Fade-Free Power

And here’s how the actual durability of the RedLithium packs has changed:

  • Operates Down to 0°F/-18°C
  • Runs 20% Cooler
  • Up to 50% More Recharges
  • No Memory Effect

Now look at the values given to the newest RedLithium High Output packs:

  • 50% more power
  • Runs 50% cooler

The Intelligence Behind Putting the Brains in the Battery Pack

So the battery pack talks to the tool. The tool talks to the battery pack. Certainly, in terms of discharge or using the power tool, on-tool protection and monitoring are again key. But each tool has to know what’s happening with its battery – what its temperature is, charge level, etc. That way each of Milwaukee’s tools will react and respond appropriately and you don’t get a “one size fits all” approach to battery management and performance. That basically means that different thresholds for different packs are also now possible.

It really is a two-way street. If Milwaukee had simply placed overload thresholds only in the pack, then the pack would perform the same whether it was used with a flashlight or a circular saw. This is not the case with RedLithium (or their original lithium-ion batteries for that matter).

Slim Packs vs XC Fat Packs

Originally, Milwaukee RedLithium battery technology set limits on the battery packs. They did this so that users couldn’t use a Slim pack with a cordless circular saw, for example. These limitations were necessary at the time. Milwaukee wanted the ability to provide users with a satisfying experience. Pairing early slim packs with higher-torque tools would have yielded saws with slower cut times, more frequent stalls, and significantly reduced run-time.

Currently, RedLithium packs handle higher temperatures and dissipate heat more easily due to the advanced cell structure and electronics. With this, the “feel” of the tool is sustained, even with less run-time and torque. Since the tools don’t run out as quickly, Milwaukee opened up all of its tools to use the newer batteries.

Milwaukee 12.0 Ah High Output and XC 5.0Ah batteries side-by-side

Milwaukee RedLithium High Output battery technology takes that even further. A High Output CP3.0 slim battery has more power and effective runtime than original RedLithium XC packs when used in high-demand tools. The larger XC8.0 and HD12.0 packs provide almost ridiculous levels of power that match or exceed what’s available in 120V corded tools.

Milwaukee XC8.0 Ah battery

Another feature of comparing older to newer Milwaukee RedLithium batteries has to do with the primary gains realized from heat dissipation and heat management. The net effect is that—the harder a tool gets pushed, the more of an increase in run-time you realize. This is a factor of how much better the power curve is realized under load.

Larger Packs Still Deliver More Power

Don’t think that this means your Slim pack will result in equal torque for your cordless drill or high power hammer drill. There still remains a noticeable power difference between a 5-cell pack vs a 10-cell pack feeding the tool. The electronics set and manage some of this. However, the tool also has a natural current draw. While it can be limited by the battery pack electronics in terms of amperes per second, it still has an effect on total power.

To demonstrate how having more cells yields greater battery efficiency, we need to set up a scenario. This applies to Milwaukee RedLithium battery technology but also other tool batteries. Let’s assume a battery pack needs to deliver 20A of current to a tool. That would yield 360W of power.

Since we’re not talking about runtime, we won’t go into how long the battery could maintain that load. However, this is not an uncommon or excessive amount of current or power to deliver for a power tool under reasonable load.

Let’s Do Some Simple Math

Here’s the equation for a slim pack with five battery cells. For reference, power is expressed in watts (volt-amps), current as amps, and voltage by volts:

I (current) = P (power) / V (voltage)

20A {5 cells} = 360W / 18V

4A {1 cell}= (360W / 18V) / 5

Realize that each cell produces 3.6V regardless of how it is configured. That’s the voltage output by the cell. An 18V battery with 5 cells means that to put out 20 amps of power, each cell needs to generate 4 amps.

Now let’s take those last two lines and look at 15 cells as in a larger 12Ah battery pack:

20A {15 cells} = 360W / 18V

1.33A {1 cell} = (360W / 18V) / 15

Adding more cells in parallel means that each cell needs to deliver much less current for the pack to output the same amount of total current as demanded. In addition to having more runtime, these larger packs can deliver more output and run at much cooler temperatures.

Run-time or torque differences are based on the pack’s ability to feed the motor. This greater current capacity “stiffens” the motor curve (at higher speed under load). This is where more torque and other advances take place with the larger 10-cell and 15-cell packs.

Milwaukee RedLithium USB Batteries

Oddly enough, larger batteries didn’t get all the attention. Smaller batteries also benefitted from advanced technology. RedLithium USB batteries make a great case in point. These advanced cells now show up in headlamps and flashlights. They deliver rechargeable and replaceable cells to devices that previously required non-removable batteries or standard alkaline cells.

RedLithium USB

What’s in Store for the Future of Lithium-ion

We asked about the future of lithium-ion, and in particular, the potential use of prismatic cells as they advance. The bottom line is that cell technology (and Milwaukee RedLithium battery technology) will continue to progress, albeit slowly. And it’s good to remember that the cell is just 1/3 of the equation. You can have the best cell plus no electronics and literally destroy a tool. Consequently, you can have a poorly constructed battery pack that shatters when dropped, spilling out all the advanced electronics and cell technology onto the ground… no good either. If you lose just one weld on a battery pack, you lose the whole thing. Lithium-ion batteries give you no partial credit!

Increased amp-hour capacity and power density continue to improve. We already have new packs with denser, larger 21700 battery cells. Also, better cell impedance results in faster charging among other things). Given that iPads are really driving more advances in prismatics we may see some movement there, but for now, it’s not likely that prismatics will come to power tools anytime soon. They tend to have cooling issues and other considerations which prevent their use.

So while tool batteries may not look different in the near future, they are bound to last longer and charge more quickly. That’s very very cool for professionals and home users alike.

Editor’s Note #2: Here are a list of phrases that didn’t make it into this Milwaukee RedLithium battery technology article:

  • “Paul seemed really charged up to talk to us about his new batteries”
  • “We ran our tools through a battery of tests…”
  • “Milwaukee really packed a lot into RedLithium…”
Your BUYING and USING Milwaukee M18 Batteries ALL WRONG! (stop doing this)

Milwaukee Battery Comparison

Milwaukee Battery Comparison

Whether you're taking on a small home improvement project or a large construction job, you rely on power tools. And for your power tools to work properly, they need long-lasting, reliable batteries and chargers. But figuring out which battery is best for your particular power tool and situation is not always easy.

For this reason, we've put together a guide introducing battery products from Milwaukee Tool, one of the leading brands in the power tool industry. These battery products vary widely in capacity, power, weight and size, so you'll have no trouble finding the perfect batteries for your application.

Battery Sizes Available

When browsing our selection of batteries, you'll notice there is either a USB, M4™, M12™, M18™ or M28™ in the product description. These terms refer to the voltage — a term we have all heard, but which not everyone understands. Voltage is the difference in electric potential between the battery's positive and negative terminals. The greater the difference in potential, the higher the voltage. Electric potential refers to the difference in charge between the battery's two terminals. One terminal is positively charged, and the terminal is negatively charged. When a terminal has a negative charge, this means it has an excessive amount of electrons, which are negatively charged particles. A terminal with a positive charge, on the other hand, has an absence of electrons.

Because of the physical separation between these terminals, the electrons cannot travel from the negatively charged terminal to the one with the positive charge. However, once you connect two terminals via a circuit, the electrons can now travel along the circuit's path, going from the negative electrode to the positive electrode. The motion of the electrons here is current, which we measure using amperes, or amps.

Milwaukee® offers batteries of five different voltage levels for power tool batteries.

1. USB

As a relatively new option, USB is a tiny battery commonly used for flashlights. The USB battery we offer is called the Milwaukee® 48-11-2130, which you can use with Milwaukee® Rechargeable products. This exceptionally long-lasting battery, which offers over 2,000 recharges over its lifespan, also boasts the following features.

  • Large capacity: This USB battery has twice the capacity of three AAA alkaline batteries.
  • Fast charge: When using a Milwaukee® REDLITHIUM™ USB Charger, it charges three times faster. You can get 50% of the full charge within 30 minutes, 80% within an hour and a 100% charge in just two hours.
  • Generous warranty: The REDLITHIUM™ USB Battery comes with a two-year warranty.
M4™ Battery

2. M4™

M4™ batteries are four-volt batteries and include products such as the Milwaukee® 48-11-2001, which is a 2.0 amp-hour REDLITHIUM™ Compact Battery Pack. It has 40% more runtime than the previously offered four-volt battery packs and can deliver up to 50% more runtime than competing products. The product is compatible with the 48-59-2001 M4 charger. M4™ products are fairly rare, as most power tools require batteries with more power, like the M12™ and M18™.

3. M12™

As one of the most commonly used sizes, M12™ batteries are, as the name suggests, 12-volt. Smaller and sleeker than their 18-volt counterparts, M12™ batteries are well-suited for those who use tools but don't require a high voltage. One M12™ battery we offer is the Milwaukee® 48-11-2420, which delivers up to twice the runtime, 20% more power and twice the number of recharges of standard lithium-ion batteries. Additional benefits of this product include the following.

  • Compact design: The battery fits in tight spaces and minimizes user fatigue.
  • Onboard fuel gauge: You can see the remaining runtime displayed on the board, meaning you'll have less downtime on the job.
  • All-weather performance: The Milwaukee® 48-11-2420 delivers fade-free power in the most extreme conditions, performing in temperatures below zero degrees Fahrenheit.
  • Maximized battery life: This battery features individual cell monitoring and a temperature management system to maximize its life.
  • Compatibility: This battery powers all Milwaukee®'s M12™ cordless power tools.
  • REDLINK™ intelligence: It provides overload protection to prevent users from damaging their power tools in heavy-duty situations. This capability is possible thanks to the total-system communication among the battery, tool and charger.

4. M18™

M18™ is the other most common battery size. Whereas M12™ is ideal for tools that require less power, the Milwaukee® battery M18™ is best for tools needed for heavier-duty jobs that require more power. This 18-volt battery features a larger design and base, which means it is a little heavier. However, depending on the power tool you're using and its application, a bit more weight may be beneficial in some situations. The Milwaukee® 48-11-1815 is a compact M18™ REDLITHIUM™ battery offering 1.5 amp-hours of runtime. Below, we will discuss many Milwaukee® M18™ batteries in depth.

M28 Battery

5. M28™

The M28™ is a 28-volt battery with limited use in a few professional-grade tools. Most applications don't require the level of power it offers.

Which Milwaukee Battery Size Is Best?

Which Size Is Best?

As mentioned above, the vast majority of power tools utilize either the M12™ or M18™ batteries, and which size you select will depend on what your tool requires. However, if you have not yet bought your tools and are trying to decide between 12-volt and 18-volt equipment, consider the following factors.

  • Power: While 18-volt tools are more powerful than 12-volt tools, you may not require all the torque of 18 volts. If you're a professional carpenter, chances are Milwaukee® battery M12™ tools will deliver the power you need. If you're in a situation that involves high-stress and heavy-duty tasks, however, Milwaukee® battery 18V tools may be more suitable for the job. Otherwise, you'll likely find 12 volts are enough for all your tasks.
  • Weight: 12-volt tools and batteries offer the advantage of being more lightweight. If you are often having to work in attics, crawlspaces and working overhead with your arm extended, you will appreciate the lighter weight of the 12-volt tools. If the power level of 12-volt tools is good enough for your purposes, you'll want to choose that platform.
  • Size: 12-volt tools are smaller. If you have limited space in your truck bed or toolbox and 12 volts will deliver the power you need, consider getting as many 12-volt tools as possible. This strategy will free up space and allow you to carry a wide variety of tools, so you can be better prepared for whatever job you encounter.
  • Charge time: M12™ batteries charge faster, which could mean less downtime on the job.
  • Runtime: The Milwaukee® battery M18™ can run for longer than M12™ batteries.
Milwaukee Battery Configurations

Milwaukee® Battery Configurations

M18™ batteries are available in three main configurations, based on the number of Li-ion cells they have.

  1. Compact (CP) battery packs: The CP battery packs feature five Li-ion cells.
  2. Extended-capacity (XC) battery packs: The XC battery packs feature 10 Li-ion cells. M18™ XC batteries can provide certain tools with a power boost, known as the "XC effect." You can expect one of these batteries to give your M18 drill a roughly 10% increase in power. XC battery packs are ideal for tools like drills, reciprocating saws, rotating saws or any tools that need a little more power to make it through tougher material.
  3. High-demand (HD) battery packs: HD batteries have 15 Li-ion cells. They deliver the longest runtime and run cooler, making them suitable for the heaviest-duty M18 cordless power tools. They are ideal for tools like miter saws, table saws or practically any outdoor power tools. This nine-amp-hour battery maintains full power, pushing cordless power tools for longer than any CP or XC battery.
Milwaukee M18 Battery Comparisons

Milwaukee® M18™ Battery Comparison

Now we're going to talk about each Milwaukee® M18™ battery pack available. But before we start, we want to make sure you're familiar with the following two terms.

  • Amp-hour: The products will be in the order of increasing charge capacity, measured in amp-hours. An amp-hour refers to how much current a battery can supply over one hour. For example, if a battery has a charge capacity of one amp-hour, that means the battery can supply current of one amp for exactly one hour, two amps for a half-hour, a third of an amp for three hours, etc., before it becomes discharged completely.
  • High output: You'll notice some of the battery packs with greater capacities contain the words "high output" in their title, which means the batteries feature larger 21700 Li-ion cells. Compare this with standard batteries, which have 18650 cells. The 21700 Li-ion battery cells, in addition to delivering a higher capacity, also provide more power and run cooler. For these reasons, M18 batteries can provide higher output than standard batteries. An easier way of thinking about it is that a high-output battery bumps you to the next level of runtime — but in a smaller-sized battery pack.

Milwaukee® CP Battery Packs

Milwaukee® offers three CP battery packs, with capacities of 1.5, 2.0 and 3.0 amp-hours.

CP 15 Battery

CP 1.5

The M18™ 1.5 amp-hour compact battery from Milwaukee®, which weighs only 0.95 lbs, has been around for many years. This lightweight, low-capacity battery is best suited for light-duty jobs such as light drilling, screw-driving and punch-list projects. For DIYers looking at Milwaukee® as a step up, this battery pack is a great, affordable choice.

CP 2.0

The 2.0 amp-hour compact battery has 33% more capacity than the 1.5 amp-hour battery, thanks to a cell upgrade that didn't come at the cost of more weight or size. At 1.1 pounds, the CP 2.0 only weighs 0.15 pounds more than the CP 1.5. Just like with the 1.5 amp-hour battery pack, the 2.0 is also a great choice for light-duty drilling, screw-driving and punch-list projects. You may even be able to pop one into a circular saw to make a few final cuts at the end of your day. If you're using heavy tools like Milwaukee® drills, SURGE™ hydraulic drivers or impact drivers, consider using 2.0 amp-hour batteries to keep down their weights.

High-Output CP 3.0

Milwaukee®'s 3.0 amp-hour high-output battery is its most advanced 1P compact battery. It uses the larger 21700-sized lithium-ion cells, enabling it to run 50% cooler and with 50% more power than the CP 1.5 and CP 2.0. It also offers twice the runtime capacity of the 1.5 amp-hour and 50% that of the 2.0 amp-hour. It boasts a smaller footprint and, at 1.33 pounds, drops the weight of the XC 3.0 by 15% with the same capacity. For this reason, it's a good choice for reducing the weight on your Milwaukee® drills, impact drivers and some cordless electrical and plumbing equipment.

Milwaukee® XC Battery Packs

Milwaukee®'s XC battery packs are available as 3.0, 4.0, 5.0 or 6.0 amp-hour batteries, allowing you to adjust your tools to any work demands.

XC 3.0

The M18™ XC 3.0 battery pack was Milwaukee®'s original 2P extended-capacity pack, and is still available in several kits. It is not as popular as the 4.0 and 5.0 amp-hour battery packs. The 3.0 amp-hour high-output battery may someday replace it, since it provides the same capacity at around half the size. At 1.69 pounds, this M18™ battery weighs significantly more than its counterpart, the CP 1.5. It is best suited for heavier tools like SAWZALLS®, rotary hammers and cordless circular saws, although larger batteries have considerably longer runtime.

XC 4.0 Battery

XC 4.0

The Milwaukee® M18™ 4.0 amp-hour battery once held the top spot as the go-to 2P pack, although the XC 5.0 has now taken its place. It offers 33% more capacity than the XC 3.0, and you can buy this battery as part of a battery/charger start kit or multi-pack. The XC 5.0 may soon entirely replace the 4.0 as the 2P pack of choice.

The 4.0 is a baseline battery for Milwaukee®'s bigger mid-level tools like SAWZALLS®, circular saws, rotary hammers, plumbing and electrical tools. For newer tools with more power, consider using the high-output or 5.0 amp-hour batteries, depending on what the tool is.

XC 5.0

Milwaukee®'s M18™ 5.0 amp-hour battery is the go-to 2P battery and perhaps the most popular battery in the entire line. Due to an upgrade to a lithium-ion cell, it boasts 67% more capacity than the XC 3.0 and 25% more than the XC 4.0, despite having about the same weight and footprint. If you own XC 3.0 batteries and they've come to the end of their useful lives, consider upgrading to the XC 5.0 batteries.

This battery can do practically anything — you can use it with your Milwaukee® impact drivers and drillers to achieve a longer runtime. You can also reasonably power most Milwaukee® M18 FUEL™ products using this battery, but keep in mind some of Milwaukee®'s newer tools will work better with high-output battery packs.

As the 5.0 is fairly lightweight, it's a good option for reducing weight when using Milwaukee® OPE tools like Quik-Lok™, although the runtime may not be sufficient.

XC 6.0

Milwaukee®'s 6.0 amp-hour high-output battery is a fantastic choice for running almost any M12 or M18 FUEL™ product, even the majority of tools that prefer a high-output pack. The only exceptions are the Super SAWZALL® and the M18 FUEL™ Table Saw if they're going to be the main tools on a long workday.

High-Output XC 8.0

The 8.0 amp-hour high-output battery is basically the 5.0 XC with its cells swapped out for the higher-density 21700s. As the most advanced 2P pack available, it has 60% more capacity than the 5.0 amp-hour battery.

As this battery is relatively large, we recommend you use it mainly for M18 FUEL™ products that prefer a high-output battery, although it also works on miter saws and rotary hammers. Compact tools and many of the lighter M18™ tools feel too heavy and unbalanced when used with this battery.

Milwaukee® HD Battery Packs

Milwaukee®'s HD battery packs, which have 15 Li-ion cells, have a reputation for their long runtime and cool operation. They are available in two options.

HD 9.0

The 9.0 amp-hour high-demand battery from Milwaukee® is the foundational power source for the company's OPE line and several other tools. While it doesn't run as cool or deliver as much power as the high-output battery, it is preferable when you need sustained power instead of faster, more powerful bursts.

High-Output HD 12.0

Milwaukee®'s 12.0 amp-hour high-output pack is the cream of the crop. Its impressive 216 watt-hours provide the user with three times the capacity of an XC 4.0. For the newest tools with the most power, this pack is the go-to battery. You can find it in kits with the 2732 circular saw, SDS-Max rotary hammers, M18 FUEL™ chainsaw and table saw.

For tools or products like lighting you don't need to carry regularly, this pack provides the longest runtime. It also gives a boost to tools such as the SWITCH TANK™, as long as the extra battery weight doesn't bother you.


1. What's the Best Milwaukee® Battery?

The best battery for your needs will depend on your specific application and priorities. To make a confident selection, consider factors like:

  • What tool you plan to use the battery with
  • Whether you prefer long runtime or short charge time
  • Whether you will need the battery to handle heavy-duty tasks

2. What Is the Difference Between Milwaukee® Batteries?

Milwaukee® batteries feature different voltages. Voltage impacts weight, charge time, runtime and compatibility with various tools. For example, a Milwaukee® M18™ provides 18 volts and lasts longer than a Milwaukee® M12™ battery, which offers 12 volts.

3. How Long Do Milwaukee® Batteries Last?

Milwaukee® batteries are designed to last for a certain number of charges. As a result, the lifespan of a Milwaukee® battery varies depending on how frequently you use it and whether you store it properly. To figure out about how long your battery will last, check the warranty.

4. Is It Bad to Leave Milwaukee® Batteries on the Charger?

Leaving your Milwaukee® batteries on their chargers will not cause damage. However, you should still unplug the charger and remove batteries soon after they finish charging whenever possible, as heat generated by the plugged-in charger can contribute to performance loss over time.

5. How Do You Store Milwaukee® Batteries?

To keep Milwaukee® batteries performing at their best, make sure to follow the instructions for storage and maintenance. In general, you should store your lithium-ion battery packs inside at room temperature. Ensure batteries are kept well away from sources of moisture, as exposure to water or excessive humidity can cause the terminals to corrode. In addition, try to avoid leaving your batteries in overly hot or cold temperatures, as this can shorten their lifespan.

Milwaukee® lithium-ion batteries last longer in long-term storage than other battery types, so you can leave them for up to one year before charging as normal. If you need to keep a battery on the shelf for the long term, store it at about 50% charge for the most stable battery chemistry.

Explore the Power Tool Battery Pack

Explore the Power Tool Battery Packs and Chargers Available Online

At Construction Fasteners and Tools, we provide our customers with the batteries and chargers they can trust to help them complete their projects. In addition to our high-quality, reliable products, we also offer the following benefits to our customers.

  • Large selection: We have a wide range of power tools, hand tools, safety equipment and much, much more. We have more than 100 brands to choose from, and even if we haven't listed the item you're searching for, there's a good chance we can — and will — get it for you.
  • Proven track record: Construction Fasteners and Tools is a locally owned and operated business, and we have been serving our community for 15 years.
  • Competitive pricing: With Purchasing Power from the Fasteners Group, we can offer competitive prices on any supplies you need.
  • Quick turnaround times: We get your orders to you as quickly as possible, with most orders shipping on the same day.
  • Free shipping on qualifying orders: We offer free shipping for Milwaukee®, Bosch, Dewalt and Makita orders over $99. Visit our site to find out more details.
  • Friendly, helpful staff: Our talented team of staff members is always eager to help. Customer service is the single most fundamental part of our business, and we believe customers buy products from people, not companies.

Let Construction Fasteners and Tools be your primary supplier for all construction, manufacturing, maintenance and industrial applications. If you have any questions or concerns, feel free to contact us by email.


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