how to choose BMS in a battery pack?

[MK2R]

Alright, i am not going to start any new threads for just asking some questions. i got my first 250 pack of untested cells, it was rather cheap, got a liitokala lii-500 battery charger / test unit on it's way, so i can't test them yet.

Most cells holds 4.14-ish V when i test them, but a few drops rapidly to way under 2V. Is there any way to save them, or are they generally screwed?

 

[john61ct]

Some will need to be tossed.

Test each cell with a CC load for mAh **capacity**.

Were these secondhand or just less than Grade A?

LiitoKala is a brand often scammed, I would only buy direct from the official Ali store

unless the seller was known to be trustworthy highly recommended by people I trust.

 

[MK2R]

i did buy the charger from a known seller, an EV-bike/scooter company locally, they also test used cells and sell untested cells (they have an income of more cells than they can test). i bought 250 ev-scooter batteries (5x50cell packs, 10S5P bms also included). i "only" paid 80 usd for this cells, so even if a lot are not working, it will still be pretty cheap per cell. so far i've tested if they hole the charge, and i have tested 100 cells, 5 of them have not been holding the charge, they drop very fast from 4v to sub 2v in matter of a few seconds.

I might save the bad cells and "test" weld on them, does it sound like an fair use of them? or should i just scrap them

 

[john61ct]

In that case there may not be any worth bothering with, or maybe 80% are scrap.

"Holding a charge" is no proper test.

Dispose EoL ones properly, they are hazmat waste, as in dangerous.

 

[MK2R]

3 of the 5 packs holds 41-41.5V charge under some load, but 2 of them holds around 37V. i am at work now so i only managed to take apart 2 of the 41+V packs, all 50 x 2 was holding the charge, the pack with 38.1? V 5 out of 50 didn't hold charge, and 45 of them did. I am expecting that the other pack with 37V will have some cells that doesn't hold any charge as well, and i hope all the cells in the last 41+V pack will be holding at least.

But i can't know for sure until i get my liitokala. i didn't hear anything really about other brands so i got a known brand, perhaps there are other battery test/chargers out there as well that are working just fine-



Would it be dangerous to weld the bad cells? just as practice to set up the welder settings