Northwestern Bell 3900 Cordless Phone Battery Ni-CD 1X4AA/L, 4.8 Volt, 700 mAh - Ultra Hi-Capacity - Replacement for Rechargeable Battery Replacement Battery for Rechargeable - Ni-CD 1X4AA/L, 4.8 Volt, 700 mAh. 100% compatible with your OEM battery - 3 year warranty. Made with high quality Japanese cells. Synergy Digital is a Registered Trademark