The Sennheiser BA 2015G2 is a rechargeable battery pack for the Sennheiser G2, G3, and G4 series wireless systems (transmitter and receiver). The battery features two rechargeable NiMH cells and is inserted into the battery compartment instead of two standard AA cells. An integrated sensor indicates battery status, monitors temperature during recharging, and avoids the charging of non-rechargeable batteries. Battery charger is sold separately.