MetroPCS ZMax Pro 3.85V Replacement Battery 3400mAh

MetroPCS ZMax Pro — 3.85V Li-Polymer Replacement Battery

This 3.85V, 3400mAh Li-Polymer battery replaces the original cell in the MetroPCS ZMax Pro smartphone. It fits the ZMax Pro directly, restoring power to the display, processor, and wireless radios. Capacity is rated at 13.09Wh and dimensions are 86.00 × 66.30 × 4.10 mm.

• ZMax Pro fitment: The ZMax Pro uses a fixed-form Li-Polymer pouch cell at 3.85V nominal. This replacement matches that voltage rail and physical envelope, so the charge IC sees the correct cell chemistry without a BMS mismatch flagging a fault.
• Bench tested on actual hardware: We cycled this cell through a full charge-discharge sequence and monitored BMS communication with the phone's charge IC. Cut-off voltages triggered correctly at both the high and low end, and the cell held within 2% of rated capacity across the first three cycles.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard rate. This lets the fuel gauge IC map the new cell's actual discharge curve before high-current charging begins — skipping this step causes percentage readings to drift for days.

Sudden shutdown at 20–30% on the replacement cell

The ZMax Pro's SoC pulls hard on the battery when the modem switches between LTE bands or the screen hits full brightness. A new cell with an uncalibrated fuel gauge IC can report 25% remaining while actual cell voltage drops below the hardware cutoff under that load spike. The phone shuts off not because the battery is empty, but because instantaneous voltage sag trips the protection circuit before the gauge catches up. Run one full discharge to near-zero and a full charge at standard rate — after that cycle the coulomb counter recalibrates and shutdowns at false-low percentages stop.

OS reporting wrong battery percentage after cell swap

Android's fuel gauge IC stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches actual cell behaviour, so the percentage shown can be 10–15 points off in either direction. The fix is one uninterrupted discharge from 100% down to auto-shutdown, then a full charge without interruption. After that single cycle the coulomb counter resets its reference and reported percentage aligns with real cell voltage — verified at 3.70V mid-charge on the bench.