Swissvoice MP40 T400 Replacement Battery 3.7V 1000mAh

Swissvoice MP40 — 3.7V Li-ion Replacement Battery (T400)

This is a 3.7V, 1000mAh Li-ion cell for the Swissvoice MP40 mobile phone. It replaces OEM part numbers T400 and T600. If your MP40 won't hold a charge or shuts down unexpectedly, this cell restores normal operation.

• MP40 cell compatibility: The MP40 uses a compact form-factor cell at 53.76 × 36.47 × 5.54mm. Both T400 and T600 share the same connector pinout and voltage rail on this handset, so this replacement covers both OEM numbers without modification.
• Bench tested on actual hardware: We cycled this cell through a full discharge and charge sequence on the MP40 platform. The BMS accepted the cell on the first connection, charge current ramped correctly through CC/CV stages, and no thermal events were recorded.
• Fuel gauge recalibration after swap: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before it starts reporting percentages to the OS — skipping this step is the leading cause of erratic percentage readings.

Why the MP40 reports wrong battery percentage after a cell swap

The MP40's fuel gauge IC stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches the actual cell chemistry and impedance. The OS reads percentage from the gauge, not the raw voltage, so you get numbers that drift or jump. One full discharge-to-shutdown followed by a full charge resets the coulomb counter and gives the IC a clean curve to work from.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops sharply under the combined load of the modem radio and screen backlight — a voltage cliff the fuel gauge didn't predict. The phone's protection circuit cuts power before the displayed percentage reaches zero. Run the handset through two full discharge-charge cycles; the gauge recalibrates its low-voltage threshold and the early shutdowns typically stop. If it persists after two cycles, check that the battery connector is fully seated — a loose contact raises effective impedance and triggers the same cliff at higher state-of-charge readings.