Sony MDR-100ABN Replacement Battery 3.7V 800mAh SP70A

Sony MDR-100ABN — 3.7V Li-ion Replacement Battery (SP70A)

This is a 3.7V, 800mAh Li-ion replacement cell for the Sony MDR-100ABN Bluetooth noise-canceling headphones. It replaces OEM part SP70A and restores full wireless and active noise cancellation function. Dimensions are 40.12 × 34.00 × 6.72mm — a direct physical match to the original cell housing.

• MDR-100ABN fit: The MDR-100ABN runs its Bluetooth radio, ANC processor, and audio amp from a single 3.7V cell. This replacement matches that voltage rail and uses the same connector orientation, so the BMS can communicate correctly with the headphone firmware without throwing a cell-mismatch fault.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the MDR-100ABN platform. The BMS accepted the pack without fault codes, and charge current stepped down correctly as the cell approached 4.2V, confirming normal CC/CV handshake behaviour.
• First-cycle charging on the MDR-100ABN: The MDR-100ABN's firmware calibrates its battery gauge against the first full charge cycle. Charge the headphones fully via USB before first use — skipping this causes the on-board gauge to misread remaining capacity for the life of that cell.

Why the MDR-100ABN cuts out mid-audio with a new battery

The MDR-100ABN draws from a single small cell simultaneously for Bluetooth transmission, ANC processing, and audio amplification. Under combined load, a cell at storage voltage — typically 3.6–3.7V out of the box — can sag below the BMS cutoff threshold even though it reads "charged." This triggers a protective shutdown that looks identical to a flat battery. One full charge cycle brings the cell to 4.2V and eliminates the sag margin that causes early cutoffs.

Battery gauge stuck at 100% then drops suddenly to zero

This happens when the MDR-100ABN's firmware has not recalibrated its fuel gauge to the new cell. The gauge was profiled against the old, degraded cell and still references those charge curves. Run the headphones down until they shut off on their own, then charge uninterrupted to full — this forces a full gauge recalibration cycle. After one complete discharge and recharge, the percentage display tracks the actual cell state correctly.