I cheated a bit: I had 2 dead batteries, one 72wh with a locked bms and a 22wh with one of the batteries dead, so I just soldered the batteries from the 1st one to the bms from the 2nd one leaving the factory welding in place. *Also, before disconnecting the original batteries I soldered another fully charged battery in parallel in order not to lock the bms, which may've been unnecessary given it didn't lock with one of the original packs showing 0v, but better safe than sorry.
As for soldering the cells, it's generally not advised, but is kinda ok if you're fast enough and have good flux. The trick is not to overheat the batteries, and that's it.
Also, I wrote a small calibration script (which is a fancy word for charging and discharging the battery a few times to let the bms know the cells have changed; mb helpful if you decide to give it a try (also there's tlp recalibrate
, but I wanted to try amber out, so here we go :D)
So, yours is core/librebooted? If it happens to be **30 series, there's also a better solution out there: https://github.com/noolex/lenovo_battery_repair