MyPhone MP-U-1 1070 Replacement Battery 3.7V 1050mAh

MyPhone 1070 / 3370 Series — 3.7V Li-ion Replacement Battery (MP-U-1)

This is a 3.7V, 1050mAh Li-ion cell built to replace the original battery in MyPhone 1070, 3370, 6651, 8815, and over 35 additional MyPhone handsets. The OEM part number MP-U-1 (also cross-referenced as MP-S-A, BS-09, MP-S-A1, and BS-16) covers the full compatibility range for this cell format. Physical dimensions are 53.00 × 33.90 × 5.60mm — verify against your original before fitting.

• Multi-model MyPhone compatibility: The 1070, 3370, 6651, and 8815 share the same battery bay dimensions, connector pinout, and 3.7V nominal voltage rail. One cell format covers all of them because the BMS handshake and charge termination voltage are identical across this handset generation.
• Bench tested on actual hardware: We ran charge and discharge cycles on the 1050mAh cell and confirmed the BMS triggers overcurrent cutoff correctly and charge termination sits at 4.2V. The cell reached rated capacity within two full cycles.
• 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 current into an uncalibrated cell — otherwise the reported percentage will drift from the real state of charge.

Why the MyPhone 1070 reports wrong battery percentage after a cell swap

The fuel gauge IC inside the phone learns a cell's discharge curve over time and stores it as a reference. When you fit a new cell, that stored curve no longer matches the fresh chemistry. The IC keeps using the old data, so it reports percentages that are off — sometimes by 15–20%. One full discharge to auto-shutdown followed by a complete charge to 100% forces the coulomb counter to reset and relearn against the new cell. After that cycle, percentage readings stabilise.

Sudden shutdown at 20–30% remaining on the replacement cell

This happens when the cell voltage drops sharply under load — typically when the modem fires up for a call or data burst, or the display hits full brightness. The fuel gauge IC predicted remaining capacity based on resting voltage, not loaded voltage, so it didn't flag the cliff coming. The cell hits the BMS undervoltage cutoff (around 3.0V under load) before the percentage reaches zero. Run one full calibration cycle first; if shutdowns continue below 3.2V loaded, the cell may have received impact damage during shipping and should be replaced.