MyPhone MP-S-A2 Replacement Battery 3.7V 750mAh Li-ion

MyPhone MP-S-A2 — 3.7V Li-ion Replacement Battery

This is a 3.7V 750mAh Li-ion replacement battery for MyPhone smartphones using OEM part number MP-S-A2. It fits devices where the original cell has aged past useful capacity or failed to hold charge across normal daily cycles. Voltage and capacity match the original spec exactly.

• MP-S-A2 platform fit: MyPhone models sharing this part number run the same 3.7V single-cell architecture with a matching connector pinout and BMS handshake protocol. Any deviation in cell voltage or connector layout would prevent the BMS from accepting the cell — this unit clears that check.
• Bench tested on actual hardware: We cycled this cell through a full discharge-charge sequence and monitored BMS communication throughout. The protection circuit responded correctly to both low-voltage cutoff and charge termination events with no rogue current draw detected.
• Fuel gauge recalibration on first cycle: On first use after installation, disable fast charging and run one complete discharge-charge cycle. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current charging loads against an uncalibrated coulomb counter.

Sudden shutdown at 20–30% on a replacement cell

This is a voltage cliff issue, not a capacity defect. Under modem or display load, the cell voltage drops faster than the fuel gauge predicts — the BMS hits its cutoff floor before the reported percentage reaches zero. The original fuel gauge IC is still calibrated to the old cell's discharge curve. One full discharge-charge cycle on the new cell resets that calibration and eliminates the premature shutdowns.

Phone not powering on after the battery sat in storage

Li-ion cells that discharge below 2.5V per cell trigger a BMS lockout to prevent damage — the phone will not respond to a normal power press. Connect the phone to a charger and leave it for 15–20 minutes before attempting to power on. The charge IC trickle-feeds current into the cell until voltage climbs back above the BMS re-enable threshold, typically around 2.9V. Once the BMS releases lockout, the phone boots and charging continues normally.