Amazon.com: Replacement for Sennheiser BA300 Battery - Compatible with Sennheiser RS 4200 RR 4200 Set 830-TV RI 830 Set 830 S RI 830 S is 410 RI 410 Headphone Battery : Electronics
Amazon.com: MPF Products BA300 BA 300 Battery Replacement Compatible with Sennheiser IS410, RI 410, RI 830, RI 830-S, RI 900, Set 830, Set 830-TV, Set 840-S, Set 840-TV, Set 900 TV Headphones : Electronics