wiimotes are not very tolerant of above 3.3v inputs(risk of fires from overheated chips in some models) they have an internal boost-only regulator for the nunchuck+motionplus that acts up above 3.3v
best use a set of diodes to offset the voltage of the lithium cell from the operational range of...
sorry bro please you are risking damage to any device you plug into the expansion connector
use a 4.2v cell and two diodes to drop the full charge voltage to 3.3v or less
the speaker issue is literally showing the chips being pushed to damage
use a schottky and a silicone didiod in series to...