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
Sennheiser BA 300 - Battery - Li-Ion - for Sennheiser RR 4200, IS 410,
Amazon.com: Cameron Sino Rechargeble Battery for Sennheiser RR4200 : Electronics