MegaFon Optima MS3B Replacement Battery 3.7V 1500mAh

MegaFon Optima MS3B — 3.7V Li-ion Replacement Battery

This is a 3.7V, 1500mAh Li-ion replacement battery for the MegaFon Optima MS3B smartphone. It fits the original battery slot and restores power to calls, messaging, and mobile data functions. Capacity is 1500mAh (5.55Wh) — matching the OEM specification for this handset.

• Optima MS3B fit: The MS3B uses a compact 64.30 x 49.50 x 4.50mm cell bay. This battery matches those physical dimensions and the 3.7V nominal voltage rail the phone's charge IC expects. A mismatch in either causes the phone to reject the cell or fail to boot.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the MS3B platform. The BMS accepted the cell without a lockout event, and the charge IC completed a full constant-current to constant-voltage taper without flagging an error.
• Fuel gauge recalibration on first install: On first use, disable any fast-charge mode and run one full discharge-to-charge cycle at standard rate. This lets the phone's fuel gauge IC map the new cell's discharge curve before high-current charging pushes into an uncalibrated state.

Why the Optima MS3B reports wrong battery percentage after a cell swap

The MS3B uses a fuel gauge IC that builds its percentage readings from a stored discharge curve calibrated to the original cell. When you install a new cell, that stored curve no longer matches the actual chemistry. The gauge reads voltage and estimates state-of-charge against the wrong reference, so it reports percentages that jump or stall. One full slow discharge followed by a full charge resets the coulomb counter and gives the IC a real baseline to work from.

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 current the cell cannot sustain at that state-of-charge. The phone's protection circuit reads a voltage cliff below the safe threshold and cuts power before the OS can log a clean shutdown. It is not a faulty battery — it is the fuel gauge IC still running an uncalibrated curve from the old cell. After one full recalibration cycle, the gauge tracks the actual voltage floor and the shutdowns stop. If they persist past two full cycles, check that the terminal voltage under load stays above 3.2V.