ONEXT Care-Phone 3 Replacement Battery 3.7V 1200mAh

ONEXT Care-Phone 3 / Care-Phone 2 / Care-Phone 4 / Active Phone — 3.7V Li-ion Replacement Battery

This 3.7V 1200mAh Li-ion cell replaces the original battery in the ONEXT Care-Phone 3, Care-Phone 2, Care-Phone 4, and Active Phone. These are compact smartphones targeted at simplified, accessible daily use. The cell measures 53.00 × 33.90 × 5.70mm and delivers 4.44Wh of stored energy.

• Care-Phone and Active Phone platform fit: These four models share a common form factor and battery bay dimensions. The connector pinout and cell footprint are consistent across the range, so one cell covers all four handsets without modification.
• Bench tested on actual hardware: We cycled this cell through charge and full discharge on the Care-Phone 3. The BMS accepted charge current from the first cycle, held voltage above 3.5V through the discharge mid-point, and triggered protection cutoff cleanly at the low-voltage threshold with no spurious trips.
• First-cycle calibration on the Care-Phone 3: After installing this cell, disable fast charging in settings for the first full discharge-charge cycle. This lets the phone's fuel gauge IC map the new cell's discharge curve before high-current charging begins. Skip this step and the percentage readout may drift by 10–15% until the IC self-corrects over several cycles.

Why the Care-Phone 3 reports wrong battery percentage after a cell swap

The fuel gauge IC on the Care-Phone 3 uses a coulomb counter calibrated against the original cell's charge and discharge curve. A new cell — even at the same rated capacity — has slightly different internal resistance and voltage behaviour. Until the IC runs at least one complete discharge from 100% to cutoff and back, the percentage display is extrapolating from stale data. After one full cycle without interruption, the gauge reanchors to the new cell and the readout stabilises.

Sudden shutdown at 20–25% on the Care-Phone 3

This happens when the cell voltage drops sharply under load — typically during a call, screen-on GPS use, or background sync — and crosses the BMS protection threshold before the fuel gauge catches it. The gauge still reads 20–25% because it is tracking charge mathematically, but the real terminal voltage has already fallen below the cutoff point. It is more common on a new cell that has not yet been calibrated, or on a cell that has aged past its usable cycle count. Run one full discharge to automatic shutdown, then charge uninterrupted to 100%, and check whether shutdowns stop — if not, check that idle terminal voltage reads above 3.6V with a multimeter before installation.