It is the battery cell or BMS that is damaged?

Hello,

I change the battery of an iphone xs max, and at first, after spot weld the old bms to new battery cells and reprogramate (with i2c i6s) the iphone did not show the 100% (on the i2c reading was reseted). Also did reset the battery health by applying an none original on iphone.

IOS was updated to date and nothing (17.5.1).

On the other day i wanted to try again, but the battery was dead and i recharge and the phone keeps turn on and off right away. Only with the fixed battery, with the none original one is ok.

So my question is, how can i know if is the bms that was damaged during the spot weld or the battery cells?

Thanks everyone for the help.

Joao Sousa