Treat weak cell phone batteries
First, the battery must be completely discharged. Then put it in a plastic bag, and close the bag properly (so that nothing comes through). Then you do the battery for a week in the freezer. After a week you get him out, let him thaw. You then connect it to a charger (but it may take a while for it to re-charge). It worked out for me. The battery had lasted twice as long. If it does not work, try two, three times, then sure.
