Chosen Solution
Hello, I have a 7000 series 42mm apple watch and the battery recently pillowed-up, so I went and purchased a replacement battery from iFixit (Item code: IF308-000-1). I swapped out the battery, but I’m having troubles with charging. Initially the battery after install was at 27%, so per the instructions I let it drain to 10% and then put it on the charger. It charged up to 100% full overnight and all seemed Ok. I wore the watch the next day and all operations seemed normal, but by the end of the day the battery was down to 27% (normally I would get two days on one charge). I placed it on the charger and this morning it is at 17% and will no longer charge up. I have tried this battery swap twice - this is my second attempt… both had the same issue and I can’t figure out what the heck is wrong. Many thanks!
I also have this issue and found that the charge controller somehow gets damaged and when this happens you need to just buy a use working unlocked one as for most it’s not repairable
Hello @Ulrich Heidenreich, So the problem is the battery controller as suspected. It is quite a bit of effort, but I replaced the old controller board from the OE battery onto the replacement lithium cell and the watch has been working well since (last 50 days). Attempt this at your own risk… With all battery soldering you need to be as quick as possible and you need to use solder that is designed for aluminum/tin that has an appropriate flux.
Unwrap the black tape from the battery management controller on the original battery.Desolder the two tabs from the controller board (needs at least 350c iron temp); Make Certain to identify and mark the polarity of the battery on the board.Repeat for the new battery and dispose of the new battery’s controller pcb.Take precautions as to not short the battery terminals together. I keep a bucket of sand on hand in case of emergency.Note that the two new batteries that I had were the the opposite polarity of the OE battery, so some bending was necessary as the edge of the lipo seal which should be the bottom of the battery needs to be at the top now. I carefully folded the tabs back on themselves at the seal and then formed them into the crease where the board will sit.Trim the new battery leads to size.Tin the tabs with the special solder and then solder back to the OE controller board.Make sure to use kapton tape to cover the leads after soldering to ensure nothing shorts after assembly.Rewrap the controller board with the original tape and foam if possible. Else some 3M double-sided foam tape can be cut down and more kapton tape can be used.
