NEC N916 Replacement Battery 3.7V 750mAh Li-ion

NEC N916 / N917 / Fly Z300 — 3.7V Li-ion Replacement Battery

This 3.7V 750mAh Li-ion cell replaces the original battery in the NEC N916, N917, and Fly Z300 handsets. All three are early-2000s candybar-style phones that share the same battery form factor and voltage rail. Capacity is 750mAh (2.78Wh), matching the original spec.

• N916, N917, and Fly Z300 compatibility: These three models use the same cell dimensions, connector orientation, and 3.7V nominal voltage rail. The BMS termination logic is identical across all three, so one cell fits all without modification.
• Bench tested on actual hardware: We cycled this cell through a full discharge-charge sequence and monitored BMS cutoff at both ends. The protection circuit tripped correctly at low-voltage cutoff and released cleanly on charge reinitiation — no latching faults observed.
• Fuel gauge recalibration on first cycle: On first use after installation, run one complete discharge down to automatic cutoff, then charge uninterrupted to 100% before using the phone normally. This gives the coulomb counter a known reference curve for the new cell — without it, the percentage readout will be unreliable for the first several sessions.

Sudden shutdown at 20–30% on the replacement cell

This happens because the phone's fuel gauge IC was calibrated against the discharge curve of the old, degraded cell. The new cell has a steeper voltage drop under modem and screen load in the lower charge window. The OS reads 25% but the cell voltage has already dropped below what the protection circuit allows under that load. One full discharge-charge cycle resets the coulomb counter reference point and eliminates most of these premature shutoffs.

Phone won't power on after the battery sat discharged in storage

Li-ion cells that drop below roughly 2.5V trigger a BMS lockout to prevent cell damage from over-discharge. The phone will show no response — no charging indicator, no boot attempt. Connect the phone to a wall charger (not a USB port) and leave it for 20–30 minutes without pressing any buttons. The charge IC needs to push a trickle current into the cell to bring it back above the BMS re-enable threshold, typically around 2.9V, before normal charging resumes.