S6 Edge - various problems after battery replacement

Hi all,

I want to start giving the old smartphones that keep accumulating in our family a second life - which primarily means replacing aged batteries.

I actually want to use my S7 as a bike computer with the Komoot app, but decided to get some practice on my wife's old S6 Edge, which conveniently partially disassembled itself (bloated battery had opened the back cover).

So I got myself a spare battery and proceeded with the disassembly. Disconnecting all connectors, replacing the battery, reconnecting everything, and putting back the 13 screws that connect the frame to the display all worked ok, and the device would start up.

Alas, there are now a few glitches:

- the device feels quite slow (at least according to my wife... but maybe that is just subjective, now being used to much more modern devices)

- the device gets really warm (primarily on the middle of the right side, i.e. where the main board is located), even without any apps running, the battery also drains quite fast

- the left touch button (which on this device brings up the "task manager"/"app switcher") does not work. The right touch button ("back") works ok, as does the home button.

Everything else seems to work fine.

I disassembled everything twice, cleaned all connectors with alcohol, reassembled, same result. All connectors appear to be properly connected.

Any idea what could have gone wrong?

Needless to say, with that not-so-great result of my first repair attempts, I hesitate to work on anything more valuable than the S6...

Regards

J