MegaFon Optima MS3B Compatible Battery 3.7V 1300mAh Li-ion

MegaFon Optima MS3B — 3.7V Li-ion Replacement Battery

This 3.7V 1300mAh Li-ion cell replaces the original battery in the MegaFon Optima MS3B smartphone. It slots into the same battery bay and connects to the same charging IC as the factory unit. Capacity is 1300mAh (4.81Wh), taken from product data — not estimated.

• Optima MS3B fit: The MS3B runs a single-cell 3.7V architecture with a shared BMS connector tied directly to the phone's fuel gauge IC. Any cell outside this voltage window causes immediate BMS rejection at power-on. This cell matches that window exactly.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the MS3B platform. The BMS accepted the cell without tripping, and the charge IC held steady through a full cycle at rated current without thermal flags.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes into an uncalibrated cell — preventing erratic percentage readings from the first hour.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff issue, not a capacity fault. When the modem or display draws a current spike, the cell voltage drops below the BMS cutoff threshold — even though the reported percentage still reads 20–30%. The fuel gauge IC is reading state-of-charge from an old calibration curve, so its estimate no longer matches the real cell voltage. One full discharge-charge cycle lets the coulomb counter relearn the actual cutoff point on the new cell — after that, the shutdown threshold aligns with real voltage, typically around 3.4V under load.

Phone not powering on after battery sat discharged in storage

If the cell voltage drops below approximately 2.5V during storage, the BMS enters lockout mode to prevent damage to the cell. The phone will show no charge indicator and will not respond to a short press of the power button. Connect to a wall charger — not a PC USB port — and leave it for at least 20 minutes before attempting to power on. Wall chargers deliver enough current to push the cell above the BMS re-initialisation threshold, typically around 2.9V, which unlocks normal charging.