Kind of what I'm seeing, but it wasn't always that way until recently when I've started using usb control with a flash drive and even though I disable the drive from the N810 and quit the program, my battery life is all over the map on the Nokia. I leave it running with plenty of battery capacity overnight, and when I wake up in the morning it's dangerously close to empty. Don't know if usb control is the cause, but it's the only thing that I've started doing different lately. I'm also switching between the original nokia battery and a mugen battery and both are doing the same thing. I've rebooted the N810 and I have not been running usb control lately to see if the N810's battery life is consistent or not and if that could be what's causing it.

This might have absolutely nothing to do with your situation, but it's funny how our battery cycle is similar where you can have a full charge and then a half day later, it'll be dead. Using USB control is the only thing that I've been using lately to test with a flash drive and even if I only watch say for example a divx movie for a couple of minutes ( which shouldn't drain that much battery juice ) and exit usb control, the battery drain will continue to kill the battery within half a day.

I'll post back if I no longer have the issue when not using usb control.