Synergy Digital Battery Compatible with Plantronics CT-14 Cordless Phone Battery Ni-MH, 2.4 Volt, 750 mAh - Ultra Hi-Capacity - Replacement for Plantronics 80639-01, 81087-01 Rechargeable Battery Replacement Battery for Plantronics 80639-01, 81087-01 - Ni-MH, 2.4 Volt, 750 mAh. 100% compatible with your OEM battery - 3 year warranty. Made with high quality Japanese cells. Synergy Digital is a Registered Trademark