I'm not going out much at the minute, so my N900s are sitting plugged into my PC via USB most of the time.

The problem is that once the battery reaches 'Full', they seem to stop monitoring the battery, and after a few days, it runs out of juice and I have to unplug the cable, plug it back in again, then wait for the N900s to have enough charge to boot before finally restarting them.

I also use 'batterymonitor', and that shows that when I plug the phone in, the number of bars remains constant (though voltage increases) until I unplug it, upon which the bars jump to their correct level.

I tried killing and restarting the bme process, but the phone's watchdog kicks in and powers it off when the bme is killed.

Can anyone think of a) what the problem is, and b) more importantly, how I can mitigate it short of unplugging them every day or so?

I have same problem too.
My device can power up only when I connect charger or plug in to PC.
when I unplug from there Led indicator still show in charge process when battery not full yet and when battery is full green LED won't turn off.after reboot process it show correct battery level.