Sony SPP-S9000 Cordless Phone Battery Ni-CD, 3.6 Volt, 600 mAh - Ultra Hi-Capacity - Replacement for SONY BP-T31 Rechargeable Battery Replacement Battery for SONY BP-T31 - Ni-CD, 3.6 Volt, 600 mAh. 100% compatible with your OEM battery - 3 year warranty. Made with high quality Japanese cells. Synergy Digital is a Registered Trademark