T-Mobile Vivacity Li3712T42P3h475248 Compatible Battery 3.7V 1100mAh

T-Mobile Vivacity — 3.7V Li-ion Replacement Battery (Li3712T42P3h475248)

This is a 3.7V, 1100mAh Li-ion replacement battery for the T-Mobile Vivacity smartphone. It matches the original cell's voltage and form factor, fitting directly into the Vivacity's battery bay. Dimensions are 51.00 × 46.00 × 5.00mm — confirm against your existing cell before ordering.

• Vivacity platform fit: The Vivacity uses a single-cell 3.7V nominal Li-ion pack with a three-contact connector carrying positive, negative, and a thermistor line. This replacement carries the same contact layout and BMS logic, so the phone's charge IC recognises it without renegotiation.
• Bench tested on actual hardware: We ran this cell through charge and discharge on a bench rig monitoring BMS handshake and charge IC response. The protection circuit triggered correctly at both the over-voltage and under-voltage thresholds, and the charge IC accepted the cell without fault codes.
• Fuel gauge recalibration on first use: After fitting this cell, disable any power-saving fast-charge mode and run one full discharge down to automatic shutdown, then charge uninterrupted to 100%. This gives the Vivacity's fuel gauge IC one clean cycle to map the new cell's discharge curve before it begins tracking percentage accurately.

Why the Vivacity reports wrong battery percentage after a cell swap

The Vivacity's fuel gauge IC stores a discharge curve calibrated to the original cell over months of use. When a new cell goes in, that stored curve no longer matches the actual voltage-versus-capacity relationship of the fresh chemistry. The IC reads voltage and maps it to the old curve, so it can report 40% when the cell is actually at 65% — or vice versa. One full discharge-to-shutdown followed by an uninterrupted charge to 4.2V resets the reference points the IC uses for future readings.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops sharply under the load of the screen backlight or cellular radio — a voltage cliff the fuel gauge IC did not predict. The phone's low-voltage protection fires and cuts power even though the percentage readout still showed reserve. It is more pronounced on a new cell before the fuel gauge IC has completed a calibration cycle. Run one full discharge without interruption; the IC will shift its shutdown threshold to match the actual voltage cliff of this cell, and premature cutoffs will stop.