INTER-TEL BT-9000 Cordless Phone Battery Ni-MH, 3.6 Volt, 650 mAh - Ultra Hi-Capacity - Replacement for Sony BP-T40 Rechargeable Battery Replacement Battery for Sony BP-T40 - Ni-MH, 3.6 Volt, 650 mAh. 100% compatible with your OEM battery - 3 year warranty. Made with high quality Japanese cells. Synergy Digital is a Registered Trademark