TeXet TM-502R Replacement Battery 3.7V 1200mAh TB-BL5C

TeXet TM-502R Series — 3.7V Li-ion Replacement Battery (TB-BL5C)

This is a 3.7V, 1200mAh Li-ion cell (4.44Wh) replacing part number TB-BL5C in the TeXet TM-502R. It also fits the TM-503RS, TM-B100, and TM-B110, plus two additional models in the same series. The cell measures 53.00 × 33.90 × 5.70mm — verify that before ordering if you are unsure which model you have.

• TM-502R series compatibility: These models share the same physical footprint, connector pinout, and 3.7V nominal voltage rail. The TB-BL5C part number covers the entire group, so one cell fits all listed devices without modification.
• Bench tested on actual hardware: We ran this cell through a full charge-discharge cycle on a TM-502R unit. The BMS accepted the charge handshake correctly, held voltage within spec under screen and call load, and showed no unexpected cutoff events during the test cycle.
• Fuel gauge recalibration on first use: After installation, disable fast charging if your device supports it and run one full discharge-to-charge cycle before normal use. The fuel gauge IC in these phones calibrates its discharge curve on the first full cycle — skipping this step causes the percentage counter to drift early in the cell's life.

Why the TM-502R reports wrong battery percentage after a cell swap

The TM-502R uses a fuel gauge IC that maps voltage curves against a stored discharge profile from the original cell. When you install a new cell, that stored profile no longer matches the actual discharge curve of the replacement. The IC continues reporting percentage based on the old data, so the number you see is out of sync with actual remaining capacity. One full uninterrupted discharge down to automatic shutdown, followed by a full charge to 4.2V, forces the IC to relearn the new cell's curve and restores accurate reporting.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff problem, not a defective cell. Under combined modem and display load, the cell's terminal voltage drops sharply at lower state-of-charge — faster than the fuel gauge IC predicts. The phone's protection circuit reads the voltage drop as a low-cell event and cuts power before the percentage counter reaches zero. Run one full calibration cycle first; if the shutdowns continue, confirm the battery compartment contacts are clean and making firm contact, as even slight resistance amplifies the voltage sag under load.