Milwaukee Battery Won't Charge Fully - FIXED! 

I have a m18 8.0 xc will this method work for me? I basically rigged my m18 to run a led light/work light and I let it run til it turned off. Went to charge just went to green light on the charger. I opened up the battery pack and I have 4 cells that are dead

I'm glad it worked for you. Thanks for the comment!

Glad it worked for you!

Thank you!

Thanks for sharing.

Sometimes an issue with a tool, but my guess is it's using it with a tool that has a heavy power draw that pulls the charge down quicker than the shut off can shut it down.

If they are fully charging, but just draining quick. You unfortunately probably just have a bad battery. I don't know of of a way to fix that.

Thanks for the comment!

Yeah, I have this exact same battery and am having the same problem. Looking around on the internet, apparently this is a SUPER common problem. I think you nailed it... the BMS just isn't working properly.

I used an eyelet style connecter for the ground on the outside and a small round style connector for the center positive.

Did it work?

Xc 8.0 same issue

Update: xc8.0 always charged only 3 bars. Did exactly what was described in this video, now the pack charges to 4 bars. Thanks a bunch !

Glad it worked for you!

I mis-spoke at the beginning of the video. Each cell is made up of 2 batteries. There are 5 sets of 2. While they do call this an 18v battery they are actually 20v when fully charged. 4x5=20

@@KonaBlueSVT Thanks

there are 5 banks of batteries, wired serially., for a total of 20.0 volts fully charged. You tested banks 1, 3 and 5. You need to go back and check 2 and 4. Ive been doing this method for several years now on the 12 Ah battery for the chainsaw. What happens is the battery management system marks banks as “bad” and no longer charges it. Why it decides they are bad i dont know, but clearly the bms is avoiding a fire hazard by shutting them down. I have “bad” banks 2, 3 and 4. I charged them individually using a 3 amp 4 volt supplies, it took 2 hours. The total voltage was 20.2 volts. Everything worked great for 3 recharges and then the problem returned somewhat. This time only banks 3 and 4 were not charging. rinse and repeat 3 charges later again a problem but this time with 2 and 4. Then i tried using an older, slow mikwaukee charger instead of the newer Fast charger type. This fixed it permanently. It takes a lot longer to charge but all the banks charge normally and fully I also have two 8.0 batteries, always using the old slow charger and never had a problem.

Because they are in series & parallel. See this link if you are unsure what that means batteryguy.com/kb/knowledge-base/connecting-batteries-in-series/

Yes, I just used 18v for the potential for higher voltage in other applications.

Thank you kindly. Super informative video easily explained. @@KonaBlueSVT

@kirkdesmond Thanks for the comment!

I believe it was a T3 tamper proof style.

It would be worth a try. Charge them slow.

When I talked to Milwaukee, they asked about what tool it was used in. They blamed it on that vs. the charger.

The batteries are supposed to have built-in protection chips. The tools don't really have any protection, and the chargers have minimal protections. When a battery is being used on any random device/tool, it should disconnect internally before the battery is too drained, and then the charging circuit (INSIDE THE BATTERY) should be still be able to negotiate with the charger and allow the incoming current in a safe way. If the battery is TOO dead, as a result of the internal battery protection not disconnecting it, then there isn't enough juice left on the battery for the internal safety boards to detect it. Since the battery COULD be missing entirely, or may only have 2 out of 10 cells present, it is just safer for milwaukee if they don't allow the chargers to force current into the battery. This is similar to a cell phone. If your phone dies, sometimes (depending on the phone and battery) you can turn it back on multiple times after the first time it shuts down on its own. It leaves that extra electricity in the battery on purpose, for the health of the battery, and to make sure the charging circuit (inside the phone and battery, NOT the wall brick) still have enough juice left to poll the sensors and regulate the charging voltage and current. You know about phone batteries and vape batteries exploding? Well, the drill batteries are the same technology, just 2-8 times bigger if they happened to explode. So, these protection circuits are important, and the manufacturer will usually err on the side of caution, because courts have sided with the "victims" and allow their insurance companies to attack the tool/phone manufacturer to recover payments used to rebuild a house that burned down. HOWEVER, this leads to a lot of batteries that simply discharged 5% too far, then stop working, and the tool company doesn't give you any core charge on these batteries that are approaching the same cost as a car battery?? You're going to see more and more videos like this, and if you do it safely, you can save a LOT of money in the long run

ru-vid.comW-Yq8_o48Yo?feature=share

Thank you boss!

One more question for you. After balancing them, how long do they stay corrected? Have they fallen back out of balance since you made the video?

So this one actually just started giving me issues again. About 10 months later.

All the components are listed in the description. Here is a video on the charger itself - ru-vid.comW-Yq8_o48Yo?feature=share

Likely stored for a long time without being charged. Once the cell falls below a threshold, the board won't charge it anymore.

@@KonaBlueSVT I measured and the biggest difference in voltage is 0.5-0.6V and that's why only three diodes lit up and the charger marked the battery as full. Cells that fall below 2.5V are permanently damaged and unsafe, so I no longer use them (short circuit and possibility of fire). The intelligent Milwaukee charger recognizes damaged cells and marks the battery as broken.

Yes, a security Torx is required.

No, it has been working normally since then.

@@KonaBlueSVT Nice.. Ill try this on my next one.. I usually just take them to work and trade them. Shhhhh lol

@@chipsammich2078 Haha, You will see them completely die sometimes, but I have had pretty good luck bringing them back using this method.

Sometimes, this works, but you may have to balance the cells like I did in this video.

So do it

The circuit board won't allow them to charge if they are under a certain voltage. So they low ones must be brought above that voltage in order to still use the factory charger.

@@KonaBlueSVT ah....Roger that

same as those 12Ah same cells

What are you using to power the converter?

@@KonaBlueSVT i bought an 120ac to 18 volt dc power converter plug like you showed in the video. it seems to be charging slowly. the power output is 4 volts at .5 amps when i test it. when i test the light is solid red. put on the battery in the correct locations and it blinks red

I have not experienced the flashing red light. Make sure your power input is not more than 8 amps. If that's not the problem and the unit is still outputting power, then I would question the buck converter itself, maybe it has an issue. These things are pretty cheaply built.

@@KonaBlueSVT i think the problem may have been, that i put the clips on first and then plugged it in. i unhooked it and turned up the amperage to 1 amp and clipped back onto the battery and it seems to be working normal now. solid red and charging. it was still charging before but it was very slow. i think when the light is flashing it puts out intermittent power in 1 second bursts when the light is on. so takes twice as long. i went from 3.5 volts on one cell to like 3.8 volts in like 7 hours

Glad you got it working!

This one went about 10 months before it started having issues again

Thank you! I used a 18v power supply from a cheap 18v tool that no longer worked.

@@KonaBlueSVT Thanks Kona!

@@KonaBlueSVT You have been so helpful, I thought I would push my luck. Would this work to power the buck converter. Super long url. www.amazon.com/Waterproof-Transformer-Adapter-100V-265V-Computer/dp/B07MZP9247/ref=sxin_16_pa_sp_search_thematic_sspa?content-id=amzn1.sym.c8697a08-4071-4b95-a6c6-18057bcdb898%3Aamzn1.sym.c8697a08-4071-4b95-a6c6-18057bcdb898&cv_ct_cx=12v%2Bpower%2Bsupply&keywords=12v%2Bpower%2Bsupply&pd_rd_i=B07MZP9247&pd_rd_r=887ad41e-105b-4760-8d0c-48d7a7067a1a&pd_rd_w=vVENg&pd_rd_wg=qyow8&pf_rd_p=c8697a08-4071-4b95-a6c6-18057bcdb898&pf_rd_r=VZYJP9JSX8GA3BYNQY4M&s=electronics&sbo=RZvfv%2F%2FHxDF%2BO5021pAnSA%3D%3D&sr=1-1-364cf978-ce2a-480a-9bb0-bdb96faa0f61-spons&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUE2STJJMU43SE82SSZlbmNyeXB0ZWRJZD1BMTA0MTQ4NjMyOElIUUlGSDFTNjYmZW5jcnlwdGVkQWRJZD1BMDg5NzgyNE1SQlBKTlczSFEyUCZ3aWRnZXROYW1lPXNwX3NlYXJjaF90aGVtYXRpYyZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU&th=1 Obviously I am not an electrician but I did wire a house once. And it hasn't burned down yet.

All I can find is a transformer that pulses, even DC. Is your 18v 1A transformer a static output of some sort??

Flashing red & green usually means the charger detects a problem with the battery. You could open it up and check it out, but I am not sure that there would be anything you can do to fix it.

@@KonaBlueSVT yeah it means error, which can also mean things like undervolt. I have some of the compact 1.5ah M12 that have a weird issue, I disassembled it and it charges, but if I press on the bottom of it or reinstall the bottom plastic cover, it stops charging and says it's full, or flashes an error, it makes zero sense.

Likely has a short or bad circuit then

2 months in, so far, so good.

@@KonaBlueSVT So you often use this battery . I had the same problem with the 9Ah battery

Yes, I've been using it weekly. I am sure it will fail again at some point. The 9AH had all kinds of problems, to the point that they discontinued them.

@@KonaBlueSVT You can check for the sake of experiment . Charge it to 100% and don't use it for ten days. And you will again have a voltage drawdown on the problem cell.

@@lutsevyat I will try that

ru-vid.comW-Yq8_o48Yo?feature=share

I am waiting for the day this one quits, but we are over 4 months and it is still working good!

To each their own. I got a new battery, AND revived this one for free.

@@KonaBlueSVThow did you get a new one ? Warranty ?

Yes, Milwaukee has awesome customer service.

@@KonaBlueSVT I’ve had mine for 2 ish years. It’s Been through a lot, wonder if they’ll still do anything with it.

@braydonkirnec1853 depending on which series it is, they have a 2 year or 3 year warranty. Check out this video for more information on that ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-RRR4mEqXO1w.htmlsi=D5o7sDBK5oWmAP8X

everyone but dewalt puts it in the battery. thats how all batteries work, they need a bms.

@@LamoidZombieDog You only need a BMS when charging. A voltage cutoff is all you need during discharge and that’s onboard. DeWalt batteries last much longer than “everyone else” because of this.

@@yolo_burrito no, DeWalt batteries do not have a voltage cutoff. This is why you have to be very careful when using them with an adapter for other tools, because they will not cut off and will undervolt. The chargers won't charge the batteries either because the voltage is so low they can't detect it (like m M12 battery at 0.5v output) or they are so discharged it's not smart enough to safely bring it back to normal voltage.

You check amperage and voltage the same way, you just change your meter settings?

@KonaBlueSVT at least with Klein, it won't read a steady current out of the buck charger, but it also pulses. That's what's making be believe the power supply is not true DC but I went through a number of them connecting the outputs to the meter, not through the buck charger, and they're all blasting nothing then flare to 1.3 amps and back down? 🤔 I can't find anything testing current this way though, usually you have to have a load and I guess the multimeter is not enough?

Do you have a 2nd meter to check it? Have you checked your meter fuse?

@KonaBlueSVT I put the meter in line with the battery connected and got a reading like you show, kept it at 1A and seems to be charging. I haven't found a meter that would measure current directly out from the buck charger, not sure how you're doing that or I'm missing something in the video, that would only work for voltage.

Unless your buck charger puts that led in the output circuit, but mine doesn't, and you can't check current using the output leads from the buck charger alone from what I can tell.

Any adjustable battery charger will work. If you discharge them down to match, the circuitry will prevent all of them from charging.

This is the most dangerous instruction I have found on the internet!!! I hope you have good fire insurance?

@@Popajaja I'm still here!

Don't do this.

Agreed. I have Milwaukee, Dewalt, and Makita. No more Milwaukee for me. This is ridiculous. They say their warranty is 3 years on batteries. They should have made an exception.

If it's in warranty.....