Infocus M2 Replacement Battery UP140008 3.8V 1800mAh

Infocus M2 — 3.8V Li-Polymer Replacement Battery (UP140008)

This is a 3.8V, 1800mAh lithium-polymer cell that replaces the original UP140008 battery in the Infocus M2 smartphone. It restores power to a phone that no longer holds charge or shuts down unexpectedly. Voltage and chemistry match the M2's charge IC and BMS requirements exactly.

• Infocus M2 fitment: The M2 uses a fixed connector layout and a BMS that monitors cell impedance on every charge cycle. This cell matches that connector pinout and sits within the impedance range the BMS expects — so the charge IC accepts it without fault codes or charge refusal.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge passes on the M2 platform. The BMS did not trip on charge acceptance, and the fuel gauge IC began tracking state-of-charge from the first completed cycle without error flags.
• Fuel gauge recalibration on first install: After fitting this cell, disable fast charging and run one full discharge down to automatic shutdown, then charge uninterrupted to 100%. This gives the coulomb counter a clean reference point against the new cell's discharge curve before normal use.

Why the Infocus M2 reports wrong battery percentage after a cell swap

The M2's fuel gauge IC stores a discharge curve calibrated to the original cell's internal resistance and capacity profile. When a new cell goes in, that stored curve no longer matches what the hardware is measuring. The result is percentage readings that jump, stall, or plateau — usually visible between 40% and 80% where the old curve diverges most from the new cell. One full discharge-charge cycle with the screen on and no fast charging resets the coulomb counter to the actual cell behaviour.

Sudden shutdown at 20–30% on the replacement cell

This happens when the modem or display triggers a current spike and the cell voltage drops sharply under load — past the BMS low-voltage cutoff — even though the reported percentage looks safe. On a new cell, this is almost always a fuel gauge calibration issue, not a faulty battery. The BMS cuts power at roughly 3.2V per cell regardless of what the OS percentage shows. Run one full discharge cycle to let the fuel gauge relearn the actual voltage-to-capacity curve, and the shutdowns will stop once the counter is tracking real cell state.