I have two 18v ryobi drill/hammer , the battery charger yelllooow light came on whitch ment baaad batery , I had read somewhere that some brands can get recond. anyway i put mine on my car charger + to + and - to - for 35 sec. put it back on the ryobi charger and wa la it charged up fine with no prob. thought i whould let everyone know . saved $60.00