About this replacement
Sena 20S / 30K / 50S / SP46 — 3.7V Li-Polymer Replacement Battery (YT102540P)
This is a 3.7V, 1100mAh Li-Polymer replacement cell for the Sena 20S, 30K, 50S, and SP46 Bluetooth motorcycle communication headsets. It matches the OEM part number YT102540P and fits the compact battery bay in each of these helmet-mounted units. Install it when the original cell no longer holds charge or the headset powers off unexpectedly mid-ride.
- 20S, 30K, 50S, and SP46 compatibility: These four headsets share the same battery bay dimensions, connector pinout, and BMS communication protocol — all four accept the YT102540P cell without modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the 20S platform. The BMS completed handshake on first charge, voltage held steady under combined Bluetooth audio and intercom radio draw, and the protection circuit tripped correctly at the low-voltage cutoff threshold.
- Intercom pairing after battery swap: Replacing the cell does not wipe saved intercom pairings on the 20S or 30K — those are stored in firmware flash, not the battery. The 50S and SP46 may prompt a firmware sync via the Sena Device Manager app after a cold-start on a new cell; run that sync before heading out.
Talk time shorter than rated on the first few charges
A fresh Li-Polymer cell ships at storage voltage — roughly 3.7V — not at full capacity. The Sena headset's fuel gauge reads from the BMS, which needs three to five full charge-discharge cycles to calibrate its capacity estimate accurately. On the first cycle, talk time will read low even if the cell is performing correctly. Run the headset until the low-battery warning sounds, then charge fully in the base dock; repeat this two more times and the reported capacity will stabilise near rated.
Headset cutting out mid-call on a new battery
This happens when the Bluetooth radio and intercom audio transmitter draw simultaneously — the combined current spike causes a momentary voltage sag that triggers the BMS undervoltage protection before the cell is actually depleted. It is most common in the first two cycles before the cell has reached full charge acceptance. Charge the headset to 100% in the dock before the next ride rather than starting from a partial charge. If cutouts continue past five cycles, check the dock contacts for oxidation — a poor contact increases impedance and worsens the sag at peak draw.