If thats a ni cad battery DO NOT mess with anything other than the OEM charger. Ni cads are prone to thermal runaway, too much current or voltage, they heat up. The hotter they get internal resistance drops, they get hotter. The result is a violent explosion and cadmium dust raining all over. I know this for fact as its happened to me, an AA size single battery exploded like an m-80, lucky I was on the other side of the room. Cadmium is very toxic.