Mitsubishi M900 Replacement Battery 3.7V 750mAh Li-ion

Mitsubishi M900 / M430i / M790i — 3.7V Li-ion Replacement Battery

This 3.7V 750mAh (2.78Wh) Li-ion cell restores power to the Mitsubishi M900, M430i, and M790i mobile handsets. These early-2000s compact phones share the same battery bay dimensions and voltage rail across all three models. If your original cell no longer holds charge or the phone shuts off unexpectedly, this is the direct swap.

• M900, M430i, and M790i compatibility: All three handsets run the same 3.7V single-cell architecture with identical connector pinout and BMS communication protocol, so one cell fits all three without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the M900 platform, confirmed the BMS handshake accepted the new cell, and verified charge termination triggered correctly at full capacity without thermal flags.
• Fuel gauge recalibration on first use: After fitting the new cell, disable any fast-charge accessory for the first full discharge-to-charge cycle. This lets the phone's fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging begins on an uncalibrated cell.

Sudden shutdown at 20–30% on the M900 after a cell swap

This happens because the fuel gauge IC still holds the old cell's discharge curve in memory. The new cell hits a voltage cliff under modem or screen load at a point the gauge still reads as 20–30%. The phone interprets the voltage drop as a fault and cuts power before the gauge catches up. One full uninterrupted discharge-to-charge cycle rewrites the curve and eliminates false cutoffs. After that cycle, the gauge should track accurately down to the real low-voltage cutoff near 3.0V.

Phone won't power on after the replacement cell sat in storage

Li-ion cells self-discharge during storage. If the cell dropped below roughly 2.5V per cell, the BMS enters lockout to prevent damage and will block normal boot. Plug the phone into a charger and leave it for 15–20 minutes before attempting to power on — the charge IC needs to push a small trickle current into the cell to bring it above the BMS re-enable threshold. If the phone still won't respond, check that the charger is delivering voltage at the port; a dead cable at this step is a common miss.