I've been experiencing the exact same problem. I even bought a brand new Nokia battery and, while it lasts a little bit longer than the original battery, the battery life is still quite short. I've reflashed the N810 many times and the problem persists. It's starting to look like it may be caused by the RX-44_DIABLO_5.2008.43-7_PR_COMBINED_MR0_ARM firmware. I'll reflash to the previous version to see if the issue goes away.