BT61-A MeiZu M681C Replacement Battery 3.85V 4000mAh

MeiZu M3 Note / Meilan Note 3 — 3.85V Li-Polymer Replacement Battery (BT61-A)

This is a 3.85V, 4000mAh Li-Polymer replacement battery for the MeiZu M681C, M681Q, Meilan Note 3, and M3 Note smartphones. It replaces OEM part number BT61-A. Capacity is sourced from the product specification — 4000mAh (15.4Wh).

• M681C, M681Q, Meilan Note 3, M3 Note compatibility: These models share the same BT61-A battery footprint, voltage rail, and connector pinout. The BMS handshake and charge IC parameters are consistent across this platform, so one cell fits all listed variants without modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the M3 Note platform. The BMS accepted the cell without error flags, and the fuel gauge IC began tracking state-of-charge within the first full cycle.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate against the new cell's discharge curve before high-current charging pushes current into an uncalibrated cell.

Sudden shutdown at 20–30% on the BT61-A replacement cell

This happens because the fuel gauge IC is still calibrated to the old cell's discharge curve. The new cell hits a voltage cliff under modem or screen load before the OS expects it. The phone reads 25% but the cell voltage has already dropped below the BMS cutoff threshold. One full discharge-to-cutoff followed by a full charge corrects the calibration — after that cycle, percentage readings stabilise.

Fast charging not working after fitting a new BT61-A

On the first charge cycle after a cell swap, the charge IC may not negotiate MeiZu's proprietary fast-charge protocol with the new BMS. This is normal — the controller defaults to standard 5V input while it characterises the new cell. Let the first cycle complete at standard rate without interruption. Fast-charge negotiation typically resumes from the second cycle onward once the BMS has logged a full charge session.