This just happened to me 3 days ago. I normally get 3-4 days of fairly light use (mostly emails and 2-3 phone calls) and then it started going to 10-20% use by the end of the day. I took my battery out and pt it back in a couple days ago and for the past 2 days I have had a full battery (85-90%) at the end of the day. Perhaps a hard boot was a coincidence, but it seems to be OK now. I was planning to get another battery, but looks like it's working OK now.