Listen portable units (LT-700, LR-500, LR-400, and/or LR-300) require either batteries or a power supply. The LA-202 Power/Charging Supply transformer plugs into any wall outlet and the POWER/CHARGING connector on the side of each unit. Receivers and transmitters can be operated using this transformer either with or without batteries. It can also be used to charge LA-362 Rechargable AA NiMH Batteries in portable products (available separately).