AHB403029 Plantronics Voyager Focus B825 3.7V Replacement Battery

Plantronics Voyager Focus B825 Series — 3.7V Li-Polymer Replacement Battery (AHB403029)

This 3.7V, 360mAh lithium-polymer cell replaces the OEM battery in the Plantronics Voyager Focus B825, B825-M, Voyager Focus 2, and Voyager Focus UC headsets. It matches the original AHB403029 pack in voltage, footprint, and connector orientation. Swap it in when the original cell no longer holds enough charge for a full day of calls.

• Voyager Focus B825 series fit: The B825, B825-M, Focus 2, and Focus UC share the same battery bay dimensions and BMS handshake protocol. All four models draw from a single 3.7V cell with the same connector pinout, so one replacement covers the range.
• Bench tested on actual hardware: We cycled this pack through the B825 charging circuit and confirmed the BMS completed a full handshake with the base station. Cell voltage at full charge measured 4.18V, within the OEM tolerance band.
• First-cycle base station charging: Seat the headset in the base station and charge it to completion before making any calls. The base needs a full charge cycle to log the new cell and begin reporting talk-time estimates accurately — skipping this causes the indicator to misread state of charge from day one.

Why the Voyager Focus B825 cuts out mid-call on a fresh battery

The B825 runs both audio processing and the Bluetooth radio from the same 3.7V cell. During active calls, that combined draw creates brief voltage sag events. If the replacement cell hasn't completed its first full charge cycle, its resting voltage sits closer to the BMS low-cutoff threshold, and a sag event trips the protection circuit. Run two or three complete charge-discharge cycles through the base station, and the BMS recalibrates its cutoff window to match the new cell's actual capacity curve.

Base station shows a full charge but the headset powers off after a few minutes

This happens when the replacement cell ships at storage voltage — typically around 3.6–3.7V — and the base station misreads that as near-full on the first check-in. The BMS hasn't completed its initialisation handshake, so the charge indicator is unreliable. Place the headset in the base, leave it charging for a full uninterrupted cycle, and wait for the LED to confirm completion. After that first cycle, the state-of-charge reading will track correctly.