Simolio SM-825D Pro Wireless Headset Compatible Battery 3.7V 600mAh

Simolio SM-825D Pro Series — 3.7V Li-Polymer Replacement Battery (SM-003-BAT)

This is a 3.7V, 600mAh lithium-polymer cell that replaces the original battery in the Simolio BIG OVER EAR wireless TV headset SM-825D Pro. It also fits the SM-829D1 and SM-829D2. Dimensions are 44.60 × 27.30 × 6.80mm — match these before fitting if you are unsure which revision of the headset you have.

• SM-825D Pro and SM-829 series fit: These models share the same cell format, voltage rail, and connector footprint. The BMS in each headset expects a 3.7V nominal Li-Polymer pack — swapping outside that spec triggers a protection cutoff at the charging IC.
• Bench tested on actual hardware: We cycled this cell through the SM-825D Pro base station and confirmed the BMS completed its handshake, accepted charge current, and released to the headset without a fault flag.
• First-cycle base station protocol: Seat the headset in the base station immediately after fitting and leave it there for a complete charge cycle before use. The SM-825D Pro base needs to log the new cell before its talk-time counter reads accurately — skipping this step causes the indicator to misreport charge state.

Base station not recognising the new pack after fitting

The SM-825D Pro base station communicates with the headset's BMS before it commits charge current. If the replacement cell arrives at storage voltage — typically around 3.6V — the base may show no charge activity or flash an error LED. This is a BMS initialisation issue, not a faulty battery. Place the headset in the cradle and leave it undisturbed for at least 90 minutes; the charging IC will trickle-charge the cell up to the threshold where the BMS handshake completes and normal charge current begins.

Headset cuts out mid-audio even with a charged cell

The SM-825D Pro draws on two loads simultaneously — the audio driver and the wireless radio. Under combined draw, a degraded or under-conditioned cell can sag below the BMS cutoff threshold momentarily, dropping audio mid-stream. This is distinct from short talk time and happens even when the indicator shows partial charge. Run three to five full charge-and-use cycles to let the cell reach its rated capacity; voltage sag under dual load reduces noticeably after the third cycle. If cut-outs persist after five cycles, check that the cell is seated flat — any pressure on the connector pin raises contact resistance and amplifies voltage sag.