I had the same problem, my N810 kept on booting when the battery was on low charge and I plugged the charger in. Nokia even swapped the device to new one, but after all it was the battery that was pretty much dead. So I ordered Mugen Power 1800mAh -battery from Holland. Problem solved. The contact surfaces of the Mugen are deeper in than the original battery, which resulted contact errors (power cutting off), but I added a piece of cardboard between the N810 and the battery to push the contacts against each other. Now the battery won't even drop out easily if I remove the backcover

http://www.mugenpowerbatteries.info/...cts/HLI-BP4LSL