Radio Shack 43-261 Cordless Phone Battery Ni-MH, 3.6 Volt, 1150 mAh - Ultra Hi-Capacity - Replacement for Panasonic HHR-P509, HHR-P401 Rechargeable Battery Replacement Battery for Panasonic HHR-P509, HHR-P401 - Ni-MH, 3.6 Volt, 1150 mAh. 100% compatible with your OEM battery - 3 year warranty. Made with high quality Japanese cells. Synergy Digital is a Registered Trademark