Can you share some photos please?
Thanks a lot
Okay, here!
Mainboard photo:
1,2,3 - simply disconnect (3 is actually battery)
4,5,6,7 - desolder 3 antennas and speaker
8, 9 - I left them connected (8 is a bit trickier to desolder, 9 will lift together with microphone)
then unscrew 2 small screws, they're also on the photo
then you turn the board over to the left - here is your battery!
Two batteries photo:
left is the original one, dead; yellow insulation removed and board unbent from the battery.
In red are the two contacts that you can simply carefully cut.
Right is new battery as is. Remove yellow tape, carefully desolder the board (DO NOT overheat the battery!).
Single battery photo:
board from old battery soldered to new battery.
Add yellow tape, fold all back, put inside, reassemble, done.