Anybody ever swap out the cells in a genuine dji battery with cells from an aftermarket battery by soldering old board to new cells thereby keeping the smart battery setup? Pulled my p4p obsidian out after a year and lost one of the batts. Opened up and read 2.25 volts across all 4 cells. She's dead Jim!
Don't know about the P4 battery - but I know that the P3 cells are strange dimensions and difficult to find ones to fit with similar capacity etc.
If you do it - you may need to sort how to get the board to recognise new cells. With the P3 - we found two contacts to short that basically reset the board .... but that was a P3 board and so long ago now - I cannot remember the two contacts.
Don't know either, but you can buy them here:
ZDF 836678 3.8V 5870mah Replacement Lipo Battery Cell For Phantom 4 Pro phantom4 battery repair and DIY 2S 3S 4S 6S
I seem to remember that lipo manufacturers use some sort of special solder. Not sure if this applies to dji batteries or not. You may want to check that out.