Replacement Sennheiser SN-BA300 Battery for Sennheiser RS 4200, IS 410, Set 830-TV, RR 4200, RI 410, Set 830 S, RI 830 Headphones (150mAh, 3.7V, Lithium-Polymer) - Walmart.com
Amazon.com : HQRP Battery Compatible with Sennheiser RR840 / RR 840, RR840-S/RR 840 S, RS4200 / RS 4200, RI830 / RI 830, RI830-S/RI 830 S, RI900 / RI 900, RR4200 Headphones/Receiver : Digital Camera Batteries : Electronics