CAT S41 Replacement Battery APP00223 3.85V 4400mAh

CATERPILLAR CAT S41 — 3.85V Li-Polymer Replacement Battery (APP00223)

This is a 3.85V, 4400mAh Li-Polymer replacement battery for the CATERPILLAR CAT S41 rugged smartphone. It replaces OEM part APP00223 and fits directly into the S41's battery bay. Use it when the original cell degrades, loses charge too fast, or begins to swell.

• CAT S41 fitment: The S41 uses a fixed-footprint bay with a specific connector orientation tied to its fuel gauge IC. This cell matches the 66.40 × 58.22 × 7.65mm dimensions and connector position, so the BMS handshake completes without errors on first boot.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on the S41 board. The BMS accepted the cell on first connection, voltage held steady under concurrent LTE and screen load, and charge termination triggered correctly at capacity.
• First-cycle fuel gauge reset: After installing this cell, disable fast charging in the S41's settings and run one complete discharge-charge cycle at standard rate. The fuel gauge IC recalibrates its coulomb counter against the new cell's actual discharge curve before fast charging pushes high current into an uncalibrated cell.

Sudden shutdown at 20–30% on the CAT S41 after a cell swap

This is a voltage cliff issue, not a capacity problem. A fresh cell has a steeper voltage drop curve than the worn cell the fuel gauge IC was trained on. When the modem fires or the screen brightness spikes, the cell voltage dips below the BMS cutoff threshold even though the reported percentage looks fine. The fix is one full discharge to 0% and a complete uninterrupted charge to 100% — this lets the coulomb counter re-map the actual voltage curve of the new cell. After that cycle, the percentage readout and the true remaining charge align correctly.

CAT S41 reporting wrong battery percentage after replacement

The fuel gauge IC stores a learned discharge profile from the original cell. When a new cell goes in, the IC continues referencing that old curve, which causes the percentage to jump erratically or plateau far above actual charge. This is not a fault with the replacement cell — it is a calibration mismatch. Charge the phone to 100% without interruption, then let it discharge fully in normal use without topping up. One complete uninterrupted cycle resets the coulomb counter and aligns the reported percentage with the cell's real state of charge.