Is your charger worn out or not working at its full capacity. This 4 V replacement battery will get your charger back in ideal working order. This replacement battery is designed for use with ESP2M-FS, ESP2M-Z, SS-440 and SS-740 chargers. Most chargers can hold a charge long after they have been unplugged or disconnected from the battery. An unplugged charger can still shock you. The consumer assumes all risk when repairing or utilizing a charger that has been "repaired" or modified. In addition, once the charger has been opened all warranties are null and void and state of federal inspections and approvals are terminated.