Stand by power WP 34s & HP 35s

[Harald]

I have no idea what kind of processor the HP35 uses, so the reason for the battery drain might be entirely different from the WP34s.
But there was an issue with floating input pins on the WP34s which Marcus corrected quite a while ago. If I remember correctly, the same problem was present in the original HP 30b firmware. Floating input pins on cmos devices can draw quite a bit of current. The problem was made much worse by installing one of my USB boards, simply because the wires acted as aerials feeding noise to the input pins.