You might not have to replace the battery - for me hooking it up to a proper li-ion 3.4v charger via wires 'revived' the battery of a seemingly dead device that was manufactured over 4 years ago that would not charge with the original glass charger. After few minutes the brush started working and was ok to go on the regular charger.

You might not have to replace the battery - for me hooking it up to a proper li-ion 3.4v charger via wires 'revived' the battery of a seemingly dead device that was manufactured over 4 years ago that would not charge with the original glass charger. After few minutes the brush started working and was ok to go on the regular charger.