Milwaukee battery out of balance

[EbikeAus]

I have a couple of Milwaukee 9ah batteries that have become unbalanced.
3 x cell groups are at 4.08v
1 x cell group is at 3.60v
1 x cell group is at 3.25v

Three leds out of 4 light up on the battery.
It still works fine on the tool and in the charger it shows green light for fully charged.
I am attempting to raise the 2 x lower cell groups to meet the rest using the IMAX charger.

Question is do you think they will retain equilibrium going forward??

I'm trying it anyway but am interested to hear opinions??

 

[EbikeAus]

Ok I've charged the 2 low cell groups.
Cells back in the case and all 4 leds are lighting up now.
I'll keep an eye on it for the next cycle then check voltages.
I was tempted to solder on balance wires but I'll wait and see how it goes first

 

[markz]

That is what the LiPo people do to rebalance them in a timely manner if they are too out of balance.
They take 2 pins and insert into the balance leads of LiPo pack to charge or discharge until equal.

 

[EbikeAus]

The next battery is probably more of a challenge, there is one group at 4.10v and the remaining 4 groups at 3.6v.
I'll probably drain the higher group with this one.

 

[999zip999]

Do not over discharge. Or leave something in the battery. Running cutoff will only unbalance a battery. As a rule.

 

[Aerialpixels]

I have the same issue and am charging the low cells with a separate charger. Trying to figure out why this happened in the first place. The BMS should be balancing the pack automatically. How did this go for you?

 

[major]

I've had good luck with Milwaukee. But had a cell fail on Craftsman C3-19.2V Li. I replaced the bad cell, just the one out of five. Used solder. As long as I had it open with tools handy, I installed a JST plug. Even though new cell is a mismatch battery seems to function o.k. I have it plugged into a meter/balancer. It also seems to work well. Battery does need help balancing occasionally. And it appeared to self discharge once.



major

 

[jonyjoe303]

tool battery packs are usually fast charged at higher amps, once cells start going out of balance, the high amps charging will be to high to let the small balance resistors to work.
Slow charging if possible might be able to get them back in balance.
Since you already open them up might as well solder balance wires on them. Those are expensive batteries a balance charger will treat them alot better then the milwaukee charger.

 

[Hillhater]

Wouldent Leaving a pack on the charger longer allow the balance to even out.?
Or is it just that the BMS’s are simply crap ?
If so, that is not good for a reputable tool company.