Unscrew the black 8mm screw holding the battery holder clip in place. Remove both the screw and the clip

Remove the two silver 5mm screws on either side of the AC adapter power jack cover.

Remove the AC adapter power jack cover itself.

Lift out the power board and unplug it from the battery connector.

When reinstalling the power board, ensure the volume slide switch engages with the prongs on the front panel switch actuator. (red box)

Capacitor C18 (47uF 6.3V, 5mm dia, 6mm height) nearly always leaks on the power board and must be replaced. It can also cause extensive damage, etching out vias and traces. See my reverse engineered power board if you want to attempt a repair.