NEC E313 Replacement Battery 3.7V 850mAh Li-ion C51-A04002-AA

NEC E313 / E616 / C606 — 3.7V Li-ion Replacement Battery (C51-A04002-AA)

This 3.7V, 850mAh Li-ion cell replaces the original battery in the NEC E313, E616, C606, and C313 mobile phones. It matches the OEM part number C51-A04002-AA and restores normal operation when the original cell degrades or no longer holds a charge. Voltage and capacity are identical to factory spec.

• E313, E616, C606, C313 compatibility: These four NEC models share the same 3.7V single-cell configuration, physical connector, and BMS handshake protocol — which is why one cell fits all four. Swapping between them requires no hardware modification.
• Bench tested on actual hardware: We cycled this cell on NEC E-series hardware and monitored BMS response at both charge termination and low-voltage cutoff. The protection circuit triggers correctly at the expected thresholds without false trips under normal screen and call load.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one full discharge-charge cycle. This lets the fuel gauge IC map its coulomb counter against the new cell's discharge curve before high-current charging pushes into an uncalibrated state.

Why the NEC E313 reports wrong battery percentage after a cell swap

The E313 uses a fuel gauge IC that stores a learned discharge curve from the original cell. When a new cell goes in, the IC still references that old curve — so it can read 40% while the actual cell state is much lower. This mismatch clears after one complete, uninterrupted discharge down to auto-off, followed by a full charge to 100% with the screen on and no interruptions. After that single cycle, the coulomb counter resets its reference and percentage readings stabilise.

Sudden shutdown at 20–30% on the replacement cell

This happens because the cell voltage drops sharply under modem or display load before the fuel gauge registers a low reading — a voltage cliff the old degraded cell masked by running flat gradually. The replacement cell has tighter voltage tolerances, so the BMS cuts power when the instantaneous load pulls voltage below 3.0V even though the reported percentage looks safe. Run one full discharge-charge calibration cycle first. If shutdowns persist after calibration, check that the battery connector is fully seated — a partial connection raises internal resistance and accelerates the voltage sag under load.