Please be aware that the SENA SRL2 Bluetooth Headset has TWO different battery versions due to regional manufacturing updates and hardware revisions:

1️⃣ 2-Wire Version: Has only 2 wires (Red & Black) leading to the plug. 

2️⃣ 3-Wire Version: Has 3 wires (Red, Black, and Yellow/White for NTC temperature sensor) leading to the plug.