CAT S30 Replacement Battery 3.8V 2900mAh Li-Polymer

CAT S30 — 3.8V Li-Polymer Replacement Battery (APP-12F-B55951-CXX-111)

This is a 3.8V, 2900mAh Li-Polymer replacement battery for the CAT S30 rugged smartphone. It fits the S30 directly and matches the OEM part number APP-12F-B55951-CXX-111. Capacity figure is taken from the product specification — 11.02Wh at the rated voltage.

• CAT S30 cell fitment: The S30 uses a sealed unibody rugged chassis with a fixed battery bay sized to this cell's 93.76 × 55.70 × 3.70mm footprint. The BMS on the S30 board communicates with the cell over a three-contact strip — voltage, ground, and thermistor. This cell carries a matching NTC thermistor so the charge IC reads temperature correctly and does not default to a slow-charge fallback mode.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on the S30 platform. The BMS handshake completed on first power-on, charge current ramped correctly from trickle to CC phase, and the charge IC did not flag an incompatible cell error at any point during the cycle.
• Fuel gauge recalibration on first install: On first use after fitting this cell, disable fast charging and run one complete discharge down to auto-shutdown, then charge fully without interruption. This lets the S30 fuel gauge IC map the new cell's discharge curve before the coulomb counter locks in its reference points. Skipping this step is the main cause of erratic percentage readings after a cell swap.

Why the CAT S30 reports wrong battery percentage after a cell swap

The S30 uses a fuel gauge IC that stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches the actual voltage-to-capacity relationship of the replacement. The IC keeps using the old curve, so the percentage readout drifts — often reading 100% for an extended period, then dropping suddenly. One full discharge-charge cycle overwrites the reference and forces the coulomb counter to recalibrate against the new cell. After that cycle, percentage readings stabilise.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops below the modem's minimum operating threshold under load — typically around 3.5V — before the fuel gauge reaches 0%. The S30's LTE modem and display draw simultaneous current spikes that cause a momentary voltage sag the aged-curve fuel gauge does not predict. The fix is the same full recalibration cycle: discharge to auto-shutdown, charge uninterrupted to 100%. If shutdowns continue after two full cycles, check that the battery contact strip is fully seated — poor contact raises internal resistance and worsens voltage sag under load.