Acer Liquid Z6 Plus BT61 Replacement Battery 3.85V 4000mAh

Acer Liquid Z6 Plus — 3.85V Li-Polymer Replacement Battery (BT61)

This is a 3.85V, 4000mAh Li-Polymer replacement battery for the Acer Liquid Z6 Plus smartphone. It replaces OEM part numbers BT61 and ATL456579. Install it when your original cell no longer holds enough charge for a full day of calls, messaging, and apps.

• Liquid Z6 Plus fitment: The Z6 Plus uses a fixed battery bay with a specific connector orientation and BMS handshake tied to the BT61 cell profile. This replacement matches that footprint at 82.30 × 64.70 × 4.30mm and communicates correctly with the phone's charge IC.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on the Z6 Plus platform. The BMS accepted the charge handshake without fault flags, and the fuel gauge IC tracked state-of-charge correctly after one complete calibration cycle.
• First-cycle fuel gauge recalibration: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle. This lets the fuel gauge IC build an accurate discharge curve for the new cell before high-current charging pushes load into an uncalibrated state.

Sudden shutdown at 20–30% on the Liquid Z6 Plus after a cell swap

A new Li-Polymer cell has a slightly different voltage-discharge curve than the degraded cell it replaces. The fuel gauge IC on the Z6 Plus is still calibrated to the old curve, so it misreads remaining capacity. Under modem or display load, the new cell's voltage drops faster than the IC expects, triggering an emergency shutdown before the reported percentage reaches zero. Running one full discharge down to automatic cutoff — then charging uninterrupted to 100% — resets the coulomb counter and eliminates these premature shutoffs.

USB fast charge not activating on the first cycle after replacement

After fitting a new cell, the charge IC on the Z6 Plus sometimes defaults to standard 5V/1A charging on the first cycle. This happens because the BMS on the replacement cell starts in a conservative state until it completes one handshake exchange with the phone's charge controller. Plug in with the original cable and charger, let the first charge run to 100% without interruption, and fast charge will re-engage on subsequent cycles. If it still does not activate, check that the USB-C port contacts are clean and the original charger is delivering above 4.5V on the data pins.