This is the second time I have experience a similar "event".
Taking the droid out of the desktop charger (with display on night mode) in showed a full charge. After a minute or two, checking txt msgs, I get a battery warning message that the power is down to 5% and the status light start to flash red. Finish reading a txt and plug in to a separate direct power supply and the indication is at 60% with full charge withing 10 minutes. The battery useage showed 85%,display, and the next minimal amount was cell waiting after the charge was complete. After the initial issue I often shut down the screen in the desktop charger, but the display is seductive.
Should I consider a routine reboot on the Droid? I am considering a backup battery, are there any extended batteries that will not void the warantee or hurt my "little friend"?