About this replacement
Sena 50R V1 — 3.7V Li-Polymer Replacement Battery (YT731958P)
This 3.7V, 800mAh lithium-polymer cell replaces the original battery in the Sena 50R V1 motorcycle communication headset. It powers the unit's Bluetooth radio, speakers, and microphone. OEM part number YT731958P confirms direct fitment to V1 hardware only — not the 50R V2.
- 50R V1 platform fitment: The V1 and V2 share a similar housing but use different cell dimensions and BMS handshake protocols. This cell measures 59.30 × 18.50 × 7.50mm and communicates with the V1 charge management circuit specifically. Installing a V2 cell in a V1 unit will result in a charging error or no charge acknowledgement from the base station.
- Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on a V1 unit. The BMS accepted the pack without error, and the base station reported correct charge state. Cell voltage at rest held at 3.82V after conditioning — within normal Li-polymer float range.
- Base station first-cycle logging: On first install, seat the headset in the base station and let it complete one uninterrupted full charge before use. The V1 base logs the new cell during this cycle to calibrate its talk-time indicator. Pulling the headset before that cycle completes can cause the indicator to read inaccurately for several weeks.
Why the 50R V1 cuts out mid-call on a new battery
The 50R V1 draws current simultaneously from its Bluetooth radio and audio amplifier during calls. On a freshly installed cell that hasn't completed its first full cycle, internal resistance is slightly elevated and the combined draw can trigger a momentary BMS undervoltage cutoff. This presents as a brief dropout or a full unit reset mid-conversation. Running two to three complete charge and discharge cycles through the base station brings internal resistance down and resolves the dropout behaviour.
Base station shows full charge but headset shuts off after a few minutes
A replacement cell ships at storage voltage — typically around 3.6–3.65V — not at full charge. If the base station's charge detection circuit reads this voltage as "charged" before completing a proper cycle, it will display a false full indicator. The headset then shuts off quickly because the cell was never fully topped up. Place the headset in the base, confirm the charge LED is active rather than static, and allow a complete charge cycle to finish before use. After that cycle, the base station will read and display charge state accurately.