300mah 500898, Hc-ba300, Nci-pls100h Battery For Sennheiser Is-410,is-4200,ri-410, Rr4200, Rs-4200, Set 830 Set 840 Set 900 - Digital Batteries - AliExpress
Sennheiser RS 4200 II Testbericht - Ladestation - YouTube
New Replacement Battery for Sennheiser RR 4200, RI 830 - Lifetime Warranty | eBay
User manual Sennheiser RS 4200 (English - 89 pages)