MeiZu M5 Note Replacement Battery BA721 3.85V 3900mAh

MeiZu M5 Note — 3.85V Li-Polymer Replacement Battery (BA721)

The BA721 is a 3900mAh Li-Polymer cell at 3.85V, built to replace the original battery in the MeiZu M5 Note and its variants. It fits the M5 Note, M5 Note Global Dual SIM, M5 Note Global Dual SIM TD-LTE, and M721C, among others. If your M5 Note shuts down unexpectedly, drains fast, or won't hold a charge, this cell is the direct swap.

• M5 Note platform fit: All covered variants share the same 3.85V rail, BA721 connector footprint, and BMS handshake protocol. The cell slots into each without modification to the charge IC or connector housing.
• Bench tested on actual hardware: We cycled this cell on the M5 Note platform and monitored BMS response through charge acceptance, load spike during screen-on modem activity, and cutoff behaviour at low state-of-charge. The BMS engaged cleanly at both ends of the voltage window.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one full discharge-to-charge cycle. The fuel gauge IC is still calibrated to the old cell's discharge curve — a slow first cycle lets it re-map against the new cell before fast charge pushes higher current into an uncalibrated state.

Sudden shutdown at 20–30% on the M5 Note after a cell swap

This is a voltage cliff issue, not a capacity fault. The fuel gauge IC still references the old cell's discharge curve, so it reads 25% while the new cell's actual terminal voltage is already dropping under modem or display load. When the cell dips below the BMS low-voltage cutoff — typically around 3.0V per cell — the phone cuts power instantly, regardless of what percentage the OS displays. Running one full uninterrupted discharge-charge cycle forces the coulomb counter to reset its endpoints against the new cell. After that cycle, the percentage readings and shutdown behaviour normalise.

Phone won't power on after sitting in storage with the new cell installed

Li-Polymer cells self-discharge during storage. If the BA721 sat discharged for weeks before installation — or the phone was left unused after swapping — the cell voltage may have dropped below 2.5V, triggering BMS lockout. At that level, the BMS refuses to pass current to protect the cell from damage. Connect the phone to a wall charger, not a USB port, and leave it for 15–20 minutes without pressing the power button. Most M5 Note BMS units will begin a trickle pre-charge recovery from around 2.5V and release the lockout once the cell climbs above 3.0V.