Mobistel Cynus F7 4G Compatible Battery 3.8V 2200mAh

Mobistel Cynus F7 4G — 3.8V Li-Polymer Replacement Battery

This is a 3.8V, 2200mAh Li-Polymer battery for the Mobistel Cynus F7 4G smartphone. It replaces the original cell when the factory battery no longer holds a useful charge or has failed entirely. Dimensions are 76.50 x 59.80 x 3.00mm — confirm clearance inside the chassis before fitting.

• Cynus F7 4G compatibility: The Cynus F7 4G runs a single-cell Li-Polymer pack at 3.8V nominal. This replacement matches that voltage rail and the physical footprint of the OEM cell, so the connector seats without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge under modem-active and screen-on load conditions. The BMS held cutoff correctly at both ends of the charge window with no unexpected trips.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes current into an uncalibrated state.

Why the Cynus F7 4G reports wrong battery percentage after a cell swap

The fuel gauge IC on the Cynus F7 4G stores a learned discharge curve from the old cell. When a new cell goes in, that stored model no longer matches the actual cell chemistry. The phone reads voltage and maps it to the old curve, so the percentage shown can be off by 10–20 points. One full discharge down to automatic shutdown followed by an uninterrupted charge to 100% resets the coulomb counter and aligns the gauge to the new cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops sharply under load — typically during an LTE data burst or a bright screen event — faster than the fuel gauge expects. The phone sees the voltage cliff as a fault and cuts power before the percentage reaches zero. It is not a defective cell in most cases; it is the gauge IC still working from the old calibration. Run one full discharge-charge cycle without interruption, then check whether the shutdowns stop. If the cell voltage at shutdown is above 3.4V on a meter, the gauge recalibration has not completed — repeat the cycle.