Bang & Olufsen EarSet 2 Compatible Battery 3.7V 140mAh

Bang & Olufsen EarSet 2 — 3.7V Li-Polymer Replacement Battery (PA-BO02)

This 3.7V, 140mAh lithium-polymer cell replaces the original power pack in the Bang & Olufsen EarSet 2 wireless Bluetooth headset. It matches the OEM part number PA-BO02 and fits the compact housing of the EarSet 2 earpiece directly. The cell measures 27.10 × 20.10 × 4.34mm and ships ready to install.

• EarSet 2 fit: The EarSet 2 runs a single-cell Li-Polymer pack at 3.7V nominal. The BMS inside the earpiece monitors cell voltage and manages charge termination through the base station cradle — voltage, cell dimensions, and connector orientation all have to match for the BMS to accept the new pack.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS accepted the pack without fault codes, terminated charge cleanly at 4.2V, and the protection circuit tripped correctly at the low-voltage cutoff threshold.
• First-cycle base station protocol: Place the EarSet 2 in the base station cradle immediately after fitting the new cell and leave it for a complete charge cycle before making a call. The base station logs the new cell during this first cycle — skipping it causes the talk-time indicator to read inaccurately for the first several uses.

Why the EarSet 2 cuts out mid-call even with a new battery fitted

The EarSet 2 draws current from two loads simultaneously during a call — the audio codec and the Bluetooth radio. That combined draw creates brief current spikes that a cell at partial state of charge may not sustain without the voltage dipping below the BMS cutoff threshold. A new cell stored for several months arrives at storage voltage, typically around 3.6–3.7V, not a full 4.2V charge. That reduced headroom means the BMS trips on those spikes before the cell is truly depleted. A full charge cycle in the base station before the first call resolves this in most cases.

Base station showing a charging error after fitting the replacement cell

The base station communicates with the earpiece BMS before it begins charging — if the BMS does not respond within the expected window, the cradle flags a charging error rather than forcing current into an unverified cell. This handshake can fail if the cell voltage is too low for the BMS to initialise, or if the connector is not fully seated. Remove the earpiece, check the connector contacts for alignment, reseat firmly, and place it back in the cradle. If the cell voltage has dropped below the BMS wake threshold, hold the earpiece in the cradle for 60 seconds — most base stations will attempt a trickle pre-charge to bring the cell back above 3.0V before switching to standard charge mode.