Composed of Nickel Metal Hydride, this battery pack is designed to function in a variety of Panasonic home phones and fax machines including the KXFG2451, KXTG5761, KXTG5771 and many more. Its NiMH chemistry allows the battery pack to hold a substantial charge, up to 850mAh, and can deliver up to 2.4 Volts of power.