Battery question

I received a number of battery packs and made my first 12v battery bank.
It's was a first trial for me, it works pretty grood for a first attempt but I need some advice.

Have my 18650 from so called dead laptop batteries. Most of these batteries have 3 x 218650 in parallel.
I tested, charged, discharged 2 cells in parallell. Is this a good way of working or should I split every single 18650 and test it's capacity?

Q2: the bank I made consists of 3x 20 cells. there's a little unbalance, like 0.12V
Tried to balance it with an imax B6 but didn't work, is this because of possible bad cell?

Thanks for your advice.




Frank - Belgium

Q1: Its perfectly fine to do that. If they have been sitting their whole life like that they most likely also are in the same level/state. There are a few out here doing that.

Q2: B6 isnt fast on balancing... At least not for big packs. If you can put them in paralell for some hours and they will balance them self
0.12v is a bit on the high side. You would like to come as close as 10mV instead of 120mV. How long did the B6 try to balance? Did it say it was done?

If you got bad cells or not properly balanced packs in terms of capacity you will see that if you for instance:

Top balance them at lets say 4.2V.

If you then drain the pack lets say 90%. If you then have 10% less in 1 of the packs that pack will be drained to lets say 3V meanwhile the others may stay at 3.4V.....

Thats when properly build packs are important. But if you stay in the middle that may not be as important but as soon as you go to its extents its important. And thats also when a BMS is good to have that can report the issue or even take care and balance them

Hi, Thanks for your feedback.

I discharged all cells and made packs with equal capacity.
Didn't fully charged them before soldering everything togehter but charged them to 3.9V

The B6 took several hours and reported balance was OK. Never checked the voltages on the B6.

Will do some more experimenting and checks, will post follow up later.

Frank