Neffos C7s Compatible Battery NBL-43A2500 3.8V 2500mAh

Neffos C7s / TP7051A / TP7051C — 3.8V Li-ion Replacement Battery (NBL-43A2500)

This is a 3.8V 2500mAh (9.5Wh) Li-ion cell for the Neffos C7s smartphone, covering model numbers TP7051A and TP7051C. It replaces the original NBL-43A2500 when the existing cell has degraded and no longer holds a usable charge. Dimensions are 76.95 × 60.10 × 4.40mm — confirm clearance before fitting.

• C7s / TP7051A / TP7051C fitment: All three model numbers share the same PCB layout, connector pinout, and BMS handshake protocol. The NBL-43A2500 part number spans the full C7s production run, so the cell and its protection circuit board are identical across variants.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a TP7051A unit. The BMS accepted charge via USB without triggering overcurrent cutoff, and the protection circuit tripped correctly at the expected low-voltage threshold — no thermal events recorded.
• 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 recalibrate its coulomb counter against the new cell's discharge curve before high-current charging pushes current into an uncalibrated cell.

Why the C7s reports wrong battery percentage after a cell swap

The fuel gauge IC inside the C7s tracks charge state using a coulomb counter — a running tally built up against the old cell's discharge curve. When you fit a new cell, that tally is mismatched from the start. The phone inherits a calibration profile that doesn't match the new cell's actual capacity or internal resistance. One full discharge-to-shutdown followed by an uninterrupted charge to 100% forces the IC to reset its reference points. After that cycle, percentage readings stabilise.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff, not a capacity issue. Under modem transmission or high screen brightness load, the cell's terminal voltage drops sharply — faster than the fuel gauge predicts — and the BMS cuts power before the displayed percentage reaches zero. It happens most often in the first few cycles when the coulomb counter hasn't yet mapped the new cell's voltage-versus-capacity curve. Run two full discharge-charge cycles without fast charging to let the gauge recalibrate. If shutdowns persist past three cycles, check that resting open-circuit voltage reads at least 3.7V after a full charge.