Voxtel M405 Replacement Battery 3.7V 1000mAh Li-ion

Voxtel M405 — 3.7V Li-ion 1000mAh Replacement Battery

This is a 3.7V, 1000mAh lithium-ion cell for the Voxtel M405 mobile phone. It fits directly into the M405 battery bay and restores power to a phone whose original cell has degraded through repeated charge cycles. Capacity is 3.7Wh — identical to the factory specification.

• M405 compatibility: The M405 uses a compact single-cell Li-ion pack at 3.7V nominal. This replacement matches that voltage rail and the physical dimensions (46.89 × 44.00 × 5.37mm), so the connector seats correctly and the BMS communicates with the phone's charge IC without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench, confirming the BMS engages charge cutoff at 4.2V and holds low-voltage protection at the correct floor. The cell accepted a standard charge profile without thermal anomalies.
• Fuel gauge recalibration on first use: After fitting this cell, disable any fast-charge mode and run one full discharge-to-charge cycle before normal use. The M405's fuel gauge IC is still calibrated to the old cell's discharge curve — one full cycle lets it map the new cell's actual capacity before reporting percentages accurately.

Why the M405 reports wrong battery percentage after a cell swap

The M405 uses a fuel gauge IC that builds its capacity model from previous discharge cycles. When you install a new cell, that stored curve no longer matches the new cell's actual voltage-to-capacity relationship. The phone reads voltage and translates it to a percentage using the old map — so it can show 40% when the cell is nearly flat, or jump from 70% to 15% without warning. One complete discharge below 5% followed by a full charge to 100% resets the coulomb counter and lets the IC re-learn the new cell's curve.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops sharply under load — the modem transmitting or the screen at full brightness draws enough current to drag voltage below the BMS cutoff threshold even though the fuel gauge still shows charge remaining. A fresh cell with an uncalibrated fuel gauge IC makes this worse, because the gauge hasn't yet learned where the voltage cliff sits on this specific cell. Run one full calibration cycle first. If shutdowns continue after calibration, check that the battery contacts in the M405 bay are clean and making firm contact — a resistive connection causes the same voltage sag under load.