M6 gone mad?

After a few years of hard use, my M6 started to have really bad battery life, so I changed it for a small li-ion cell phone battery. Worked ok, but as the unit had gone trough really rough ride, it started to show some oddities, like switching off when inserting usb, switching off during use, screen acting weird, tilting when switching to radio and so on...

And the worst thing now, the screen randomly goes almost blank, showing horizontal lines or so, and the sound distorts and playback slows down. A light tap on the unit usually helps, but lot of times it just starts stuttering and goes to full tilt. So for those cases I made a jumper for the battery wire that I can reset it.

So do you think it is my battery causing this, or may there be some cracks or damage on the pcb (looks fine though) or could it be my display going?

I am about to try again with the original battery, if I can get it to charge. Also there isn't a "sensor" wire for the battery, despite the battery safety circuit has an "S" solder point. This is by design, right?

EDIT: Put back the original battery, was the same. Once the player freezes, it needs to be reset (cut battery power). Could it be that it has gone faulty because of static discharges?

Some times the player just freezes and there is artifacts on the screen...

Sorry to hear your issue.
My guess could be broken touchpad cable like what happened to me a few years ago. The flex going from screen and touchpad to pcd are paticular weak in my eyes.