About this replacement
3M TAC300 / TAC500 Series — 3.7V Li-ion Replacement Battery (ALPHA1100)
This 3.7V, 900mAh Li-ion cell replaces the original ALPHA1100 battery in the 3M TAC300, TAC300-OTH, and TAC500 wireless headsets. It restores power to the headset's audio and DECT radio transmission circuitry. Capacity matches OEM spec at 3.33Wh.
- TAC300 and TAC500 platform fit: Both headset variants share the same 3.7V single-cell architecture, connector pinout, and BMS handshake protocol — which is why one cell covers the full model range including the TAC300-OTH variant.
- Bench tested on actual hardware: We cycled this cell through the TAC300 base station and monitored BMS communication during charge initiation. The protection circuit engaged correctly at cutoff voltage, and the base station registered a valid pack on first dock without error.
- First-cycle base station protocol: Dock the headset in the base station and allow a complete, uninterrupted charge cycle before making your first call. DECT headsets log the new cell during this cycle — skipping it causes the talk-time indicator to report inaccurate readings for several sessions.
Base station not recognising the new pack after swap
The TAC300 base station verifies the battery pack via a BMS handshake before it begins a charge cycle. If the cell ships at storage voltage (typically around 3.6–3.65V), the base may flag an error or show no charge activity on first dock. Remove the headset, wait 10 seconds, and re-dock it firmly — this resets the handshake sequence. If the error persists, the cell usually needs a brief trickle pre-charge; leave it docked for 20 minutes and the BMS will clear the fault and enter normal charge mode.
Headset cuts out mid-call on a freshly charged battery
The TAC300 draws from two loads simultaneously — the speaker driver and the DECT radio transmitter. Under combined draw, a cell with insufficient conditioning can sag below the BMS cutoff threshold, triggering a shutdown even when the indicator shows charge remaining. This is most common in the first three cycles on a new cell. The fix is straightforward: complete five full charge-discharge cycles through normal headset use, and the cell's internal resistance drops enough to hold voltage stable under dual-load conditions.