I have this as well on my 7500. I had fully charged before i got to bed last night and turned it off. This morning i ran it down to 19% and turned it off for 5,5 hours. Guess my surprise when i turned it on again and it said 64% remaining. I have tried all afternoon now, and every time it says it's under 15% i turn it off for 5 minutes and turn it back on, and it's back up to a bit over 50%, and draining fast. I'm gonna try to drain the battery as much as possible and then turn it off for an hour, charge it over night and turn it off for 5 hours and see what happens.