it stops charging when full but drops to 90% then charges full, then drops, so if it does it for extended periods of time your "full" charge will only be 10% percent of the orginal cell capacity. There are TONS of debates on battery charging protocol. In my experience, its always best to take off charger once its fully charged, the only time i keep it on the charger is at night when im sleeping... Ive never had to replace a battery under warranty