To be clear, this is a PMS Lite.
I made another go with both cells, reading 4.1v each.
If I connect 3.3v to nothing, a voltmeter reads 3.3v on power up.
If I connect everything other than the wii, 3.3v is stable.
If I connect the wii, with or without the rest, the 3.3v line reads about 100mV...