NEC E313 Replacement Battery 3.7V 1700mAh C51-A04002-AA

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

This is a 3.7V, 1700mAh Li-ion replacement cell for the NEC E313, E616, C606, and C313 mobile phones. It replaces OEM part number C51-A04002-AA. Fit it when the original cell no longer holds a charge or fails to power the device.

• Cross-model fit — E313, E616, C606, C313: These four NEC handsets share the same battery bay dimensions, 3.7V nominal voltage rail, and connector pinout, which is why a single cell covers all four. The BMS handshake protocol is identical across the group.
• Bench tested on actual hardware: We cycled this cell through full discharge and charge on the E313 platform. The BMS accepted the charge IC handshake without fault codes, and cell voltage held within spec at the 3.7V nominal rail throughout the test cycle.
• 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 against the new cell's discharge curve before high-current charging pushes current into an uncalibrated cell.

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

The E313 uses a fuel gauge IC that builds a discharge model from the original cell's coulomb count history. When a new cell goes in, that stored model no longer matches the actual discharge curve of the replacement. The gauge will read the new cell against the old curve and report inaccurate percentages — often showing full charge well before the cell is actually full, or dropping suddenly. One full discharge-to-shutdown followed by an uninterrupted charge to 100% forces the IC to reset its reference points against the new cell.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff issue, not a capacity fault. Under the load spike from the modem radio or screen backlight, the new cell's voltage drops below the BMS cutoff threshold — even though the fuel gauge still shows 20–30% remaining. It happens most often in the first few cycles before the gauge IC has recalibrated. Run the phone through two complete discharge-recharge cycles without interruption. If the shutdowns continue past cycle three, check that resting cell voltage reads at least 3.7V on a multimeter after a full charge.