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
SENNHEISER EKI 830 - Bodypack infrared receiver for two channel/stereo (2.3/2.8 MHz) systems. Includes BA300 rechargeable battery. Requires headphones or induction neckloop (ordered separately).
SENNHEISER BA 300 - Rechargeable battery for Set830(S), Set840(S), Set900, IS410, HDI830, EKI830, RI410, RI830/830S, RI840/840-S, RI900
Sennheiser BA BA 2015 battery - NiMH - 009950 - Phone Accessories - CDW.com
3.7V 140mAh BA-300 Rechargeable Battery For Sennheiser IS410 RI410 RI410TV RS4200 Bluetooth Headset HC-BA300 NCI-PLS100H 500898 - AliExpress
BA300: 3.6v-3.7v 140mAh LiPO battery pack for Sennheiser — Batteries America