Plantronics CS-50, CS50-USB Battery 3.7 V 300 mah Li-Ion,

Replacement battery compatible with Plantronics CS-50, CS50-USB, CS55, CS-60, HL10, CS351N, CS351/N, CS361N, CS361/N DECT Wireless Headsets.
Replaces battery models 65358-01, 64399-01, 64327-01, PLN-6439901, 6535801, ED-PLN-6439901.

This battery has a higher capacity than the original battery offering a longer run time before requiring recharging.
BTB-PL-64399-01