NEC N600 Replacement Battery 3.7V 900mAh Li-ion

NEC N600 / N600i — 3.7V Li-ion Replacement Battery

This is a 3.7V 900mAh Li-ion cell for the NEC N600 and N600i mobile phones. It replaces the original battery when the cell can no longer hold enough charge for daily use. Voltage and capacity match the original specification exactly.

• N600 and N600i compatibility: Both handsets share the same battery bay dimensions, voltage rail, and connector pinout. One cell fits either variant without modification.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the N600 platform. The BMS held cutoff voltage cleanly at both the top and bottom of the charge curve, with no premature trips observed during the test sequence.
• Fuel gauge recalibration after swap: On first use after fitting this cell, run one complete discharge-to-charge cycle with fast charging disabled if available. This gives the phone's fuel gauge IC time to map the new cell's discharge curve before any high-current charging begins.

Sudden shutdown at 20–30% on the replacement cell

Early shutdowns at 20–30% are a fuel gauge calibration problem, not a faulty cell. The phone's coulomb counter is still referencing the discharge curve of the old, degraded battery. When the new cell's actual voltage drops below the threshold the IC expects at that percentage, the phone reads it as a critical low and cuts power. Running one full discharge down to automatic cutoff — then charging uninterrupted to 100% — resets the reference curve. After that cycle, the reported percentage should track the actual cell state accurately.

Phone will not power on after sitting in storage with this battery fitted

If the phone was stored with the battery installed and unused for an extended period, the cell voltage may have dropped below 2.5V. At that level, the BMS enters lockout to prevent damage and the phone will not respond to the power button. Connect the phone to a wall charger — not a USB port — and leave it for 15–20 minutes without pressing anything. The charge IC needs to push a trickle current into the cell to bring voltage back above the BMS recovery threshold of approximately 2.9V before normal charging and boot will resume.