About this replacement
ZTE Blade A6 Max / Blade Max 2s — 3.85V Li-Polymer Replacement Battery (Li3939T44P8H856743)
This is a 3.85V, 3900mAh (15.02Wh) lithium-polymer cell that replaces the original internal battery in the ZTE Blade A6 Max, Blade Max 2s, and Z6410S. It fits the internal bay directly, matching the OEM part number Li3939T44P8H856743. Replace this when the original cell no longer holds a charge or causes unexpected shutdowns.
- Blade A6 Max / Blade Max 2s / Z6410S compatibility: These three models share the same battery bay dimensions, connector pinout, and BMS handshake protocol. The Z6410S is a carrier variant of the same platform, so the same cell works across all three without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the Blade A6 Max platform. The BMS accepted the cell on first insertion, charge current ramped correctly from trickle to CC/CV, and the protection circuit tripped at the expected cutoff voltage under load.
- Fuel gauge recalibration on first cycle: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes current into an uncalibrated cell.
Sudden shutdown at 20–30% on the Blade A6 Max after a cell swap
This happens because the fuel gauge IC is still running the discharge curve from the old, degraded cell. When the new cell hits a voltage the old curve didn't model correctly, the OS reads a false low-battery state and the phone shuts off. The fix is one full calibration cycle — drain the phone until it powers itself off, then charge uninterrupted to 100% without fast charge enabled. After that single cycle, the coulomb counter recalibrates against the new cell and percentage readings stabilise.
USB fast charge not activating on the first cycle after replacement
On first insertion, the charge IC treats the new cell as an unknown and defaults to a slow trickle rate until it reads a valid BMS response. This is normal — the handshake between the phone's PMIC and the new BMS can take one full charge cycle to complete. If fast charge still doesn't activate after the first full cycle, clear the battery stats in developer options and repeat. Confirm the charger output reaches at least 5V/2A before ruling out the cable or adapter.