Dead battery pack

[RetiredAutoTech]

I finally found a control board for a Milwaukee 12 ah battery I have been repairing. When I got it, the pack had 6 cells at 0 volts and I tested the other 9 cells and they were at 80 percent of thier rated ah. So I decide to just buy 15 cells and replace all of them. Put it all back together and the bms wouldn't start back up. I found a new one at ali and waited 2 months for it to show up. So I tested the cells that I had soldered in to the battery pack before installing the new board. First row measured 3.49 volts. The next 4 rows showed 0 volts. I don't know if the bms drained them or I possibly used to much heat and damaged them. I tried a slow charge with my power supply at .5 amps and 2 volts on each of the rows and they climb to about .45 volts and slowly drop in an hour to .25 volts. Even the 3.49 row won't go over 3.6 volts. Next step I want to try is unsoldering all the cells and try to charge separately.

Any ideas?

 

[OffGridInTheCity]

So I decide to just buy 15 cells and replace all of them. Put it all back together and the bms wouldn't start back up.

Sounds like you left things in this state... new cells + suspicious BMS sounds like.

I found a new one at ali and waited 2 months for it to show up. So I tested the cells that I had soldered in to the battery pack before installing the new board. First row measured 3.49 volts. The next 4 rows showed 0 volts. I don't know if the bms drained them or I possibly used to much heat and damaged them.

I've never damaged a cell by soldering - so I'd put that lower on the list.

More likely - the new cells were drained to 0v (same as what you originally found) by the old BMS. Draining cells to 0V is more often than not catastrophic - destroys the cells.

I tried a slow charge with my power supply at .5 amps and 2 volts on each of the rows and they climb to about .45 volts and slowly drop in an hour to .25 volts. Even the 3.49 row won't go over 3.6 volts.

A typical 0v destructive pattern is that even if you coax them to charge they will be self-dischargers.

Next step I want to try is unsoldering all the cells and try to charge separately.

Well - not just charge but test them. At least charge them up to full charge and let sit for a week to see if they self-discharge.

 

[RetiredAutoTech]

Waste of 90 dollars if they are trashed. Going to try to save some this weekend. I have since saved about 50 of the 4000 mah inr21700-40t so I can still save the battery.

Have close to 540 inr21700-30t recovered so I can at least make a 14s 44p battery. Should be around 130 ah, hopefully I have more of these before the end of the year. Now have to work on the 5 boxes of 18650 dewalt packs I have. Maybe get enough for a second 130 ah battery.