Sony SBH-20 Compatible Battery 3.7V 110mAh Li-Polymer 381424

Sony SBH-20 — 3.7V Li-Polymer Replacement Battery (381424)

This is a 3.7V 110mAh Li-Polymer cell for the Sony SBH-20 Bluetooth stereo headset. It replaces OEM part numbers 381424 and AHB441623. If your SBH-20 is cutting out during calls or no longer holding a charge, this cell restores full function.

• SBH-20 fit: The SBH-20 runs a compact Li-Polymer cell on a 3.7V nominal rail. This replacement matches the original cell dimensions (25.00 × 14.50 × 3.80mm), connector pinout, and BMS communication protocol — so the headset's charge indicator and low-battery alerts behave exactly as they did with the factory cell.
• Bench tested on actual hardware: We cycled this cell through charge and audio-plus-radio draw on the SBH-20 platform. The BMS held the cutoff voltage correctly at low charge and did not trip under the combined Bluetooth radio and audio amplifier load that typically stresses small headset cells.
• First-cycle conditioning on the SBH-20: After fitting, charge the headset in the base station for one complete cycle before using it for calls. The SBH-20 base needs to complete a full charge pass on the new cell before its talk-time estimate registers accurately — partial charges in the first session will produce misleading low-battery warnings.

Why the SBH-20 cuts out mid-call even with a charged battery

The SBH-20 combines a Bluetooth radio burst and an audio amplifier draw at the same moment during active calls. On a degraded or storage-voltage cell, that combined current spike pulls the terminal voltage below the BMS cutoff threshold — and the headset drops. The radio draw alone is manageable, but the two loads together can exceed what a weak cell can deliver cleanly. A fresh cell with a completed first-cycle charge resolves this — the resting voltage sits high enough that brief peaks no longer trigger the cutoff.

Base station showing a full charge but headset dies after a few minutes of use

This happens when a new or long-stored cell arrives at storage voltage — roughly 3.6–3.7V — and the base station interprets that starting voltage as nearly full, ending the charge pass early. The cell never reaches a true full charge, so usable capacity is far below rated. Fix this by placing the headset in the base for an uninterrupted charge session of at least two hours with no calls taken. After one full pass, the base charge circuit re-calibrates and the cell will reach the correct 4.2V charge endpoint.