HQRP Battery for Sennheiser RR 840 / RR 840 S / RR 4200 / RS 4200 | eBay
300mAh 500898, HC-BA300, NCI-PLS100H Battery For Sennheiser IS-410,IS-4200,RI-410, RR4200,
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
300mAh Battery 500898, HC-BA300, NCI-PLS100H For Sennheiser IS-410,IS-4200,RI-410, RR4200, RS-4200, Set 830 Set 840 Set 900 - AliExpress
Sennheiser BA300 BA-300, Set 830-TV, RI 830, Set 830 S, RI 830 S, IS 410, RI 410, RS 4200, RR 4200 battery | Unicell
Amazon.com: 2 Pack Replacement for Sennheiser RS 4200 Battery Compatible with Sennheiser BA300 Set 830-TV RI 830 Set 830 S RI 830 S is 410 RI 410 RR 4200 Headphone Battery (150mAh 3.7V Lithium Polymer) : Electronics