M18 12 amp battery not charging possible fix.

[mreisner]

I have a four year old not used more than probably 25 times M18 12 amp hour battery that wouldn't take a charge, just flashed the red and green. I checked the voltage and it showed over 18 volts so I'm assuming it had the unbalanced cell problem. I went to take it apart and even though I have a T8 security bit it didn't want to budge the two screws that had the security pin in them so I'm assuming they have some lock tight on them. Videos I have seen on the internet show guys charging individual cell groups that were in the two Volt range up to four or whatever it's supposed to be. Figuring I had nothing to lose I drained the battery down with an old test light and got it to 15 volts. I tried charging it and it still gave me the error lights. For the hell it I figured I should bring it up a couple of volts and try charging it again. I jumped it off of a known good 8 Amp Hour M18 battery using my Power Probe that way it would be fused and also I could see the voltage on the Power Probe so I didn't overcharge. It didn't take more than a few seconds and it was up to 18 volts. I put it on the charger and it started charging. It's a slower older charger so it's going to take a while but in the morning I should know if I have a good battery or not. If it works great, if not I'll take it apart and do the individual charging of the low cells that were unbalanced.

 

[mreisner]

Battery was fully charged this morning at 19.98 volts, I put it on a Rover light and going to let it run down again to where it should shut itself off and then charge it again but I think that worked.

 

[Beerhippie]

Any battery rescue story that doesn't end with flames is a good story.

 

[mreisner]

Okay I have a little bit more to add. First time after charging I ran a battery on a light for a while and it wouldn't take a charge again, it did the same thing again. I discharged it with the test light to approximately 17 volts again and brought it back up with the Power Probe and put it on the charger and it took a charge. This time I discharged it on the fan I had and when it was done running the fan I put it back on the charger and it started charging as normal. Apparently it takes a couple charged discharge Cycles to balance out the cells again. Currently I've got it running on a fan for the third time just to make sure it's good. Originally I was going to open it up and charge the low cells with an RC car type charger, but the saved having to buy one and open up the battery and charge the individual packs that were unbalanced. Hopefully this is a long-term fix, I believe it is.

 

[theoldwizard1]

Any multi-cell battery back, regardless of what chemistry, should really charged with a special battery balance charger. This is to make certain that each cell is charged INDIVIDUALLY to 100% ! Unfortunately, the Milwaukee batteries and charges do not do this !

There are multiple videos on YouTube (search for "m18 battery balance") that discuss this and how to solve the problem.

Apparently it takes a couple charged discharge Cycles to balance out the cells again.

Not a guaranteed solution.