This product is either discontinued or we cannot get that from suppliers.
Poly Plantronics Spare Battery With Removal Tool 202599-03, Proprietary Battery Size, Battery Savi/CS510/520/710/720.
Replacement Battery for Plantronics W410, W410-M, W420, W420-M, W710, W710-M, W720, W720-M, CS510, CS520, CS510-XD and CS520-XD Wireless Headset Systems.