Here is the
battery guide. But from what I have been told they last so many "charge hours" so if you charge it 10 minutes every hour for a day, you only took 2 "charge hours" off it's life span. If you drain it and it took 2 hours to charge you still used 2 "charge hours" off it's life span. So don't be afraid to keep it topped off, it works better that way.
