MyPhone MP-S-A2 Compatible Battery 3.7V 550mAh Li-ion

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

This is a 3.7V, 550mAh Li-ion cell that replaces the OEM MP-S-A2 battery in MyPhone smartphones. It fits the same footprint at 53.00 × 34.00 × 4.80mm and connects to the same charge circuit. Use the Capacity field value — 550mAh (2.04Wh) — as the reference spec for this cell.

• MP-S-A2 platform compatibility: MyPhone devices using the MP-S-A2 share a common battery bay size and connector pinout. The BMS handshake on these phones reads cell voltage directly — no proprietary authentication token — so a correctly specced replacement cell is accepted on first boot.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a MyPhone unit running the MP-S-A2 spec. The BMS held charge termination at 4.2V and low-voltage cutoff fired cleanly before the cell dropped below 3.0V under load.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one full discharge-to-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before reporting accurate percentages. Skipping this step often causes the OS to display incorrect capacity readings for the first several cycles.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff failure. At 20–30% state of charge, the new cell's voltage drops sharply under the combined load of the modem radio and screen backlight. The phone's power IC interprets this as a critical low-voltage event and shuts down before the fuel gauge reads zero. The root cause is the fuel gauge IC still using the discharge curve from the old, degraded cell. Run one full discharge cycle without fast charging — this recalibrates the coulomb counter against the new cell and shifts the cutoff point back to the correct voltage floor near 3.4V.

Device not powering on after the battery sat in storage

Li-ion cells self-discharge over time. If the MP-S-A2 cell dropped below 2.5V during storage, the BMS will lock out charging as a protection measure. The phone will show no response — no charging indicator, no boot screen. Connect to a 5V charger and leave it for 15–20 minutes without attempting to power on. Most BMS circuits on this platform allow a trickle pre-charge recovery once the charger is detected, which brings the cell back above the 2.5V re-enable threshold before normal charging resumes.