Caterpillar S50c Replacement Battery 3.75V 2600mAh Li-Polymer

CATERPILLAR S50c — 3.75V Li-Polymer Replacement Battery (A09QA008H)

This is a 3.75V, 2600mAh Li-Polymer cell for the CATERPILLAR S50c rugged smartphone. It replaces OEM part numbers A09QA008H and 023.B0008.0061. If your S50c is draining faster than it used to or shutting down unexpectedly, this cell restores capacity to original spec.

• S50c platform fit: The S50c uses a sealed housing with a proprietary connector layout and a BMS that monitors cell voltage and temperature. This cell matches the original voltage rail and connector, so the BMS handshake completes without triggering a protection fault on first boot.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on S50c hardware. The BMS accepted the cell without error codes, charge current stepped down correctly at 4.2V, and the protection circuit tripped as expected at low-voltage cutoff.
• Fuel gauge recalibration on first use: On first installation, disable fast charging and run one complete discharge-to-charge cycle at standard current. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current charging pushes amps into an uncalibrated cell.

Sudden shutdown at 20–30% on the S50c after a cell swap

The S50c's fuel gauge IC stores a discharge curve calibrated to the original cell. A new cell has a slightly different impedance profile, so the gauge misreads remaining capacity and the phone hits voltage cutoff before the display reaches 0%. This is not a fault with the replacement cell — it is the coulomb counter working from stale reference data. One full discharge cycle, draining the phone until it powers off automatically, then charging uninterrupted to 100%, resets the reference point. After that cycle, the shutdown threshold aligns with the actual cell voltage floor.

USB-PD fast charge not activating on the first cycle after replacement

After a cell swap, the S50c's charge IC may default to standard 5V/1A current on the first charge cycle while it verifies the new cell's internal resistance. Fast charging requires the BMS to confirm the cell is within safe impedance limits before stepping up current. If fast charge does not activate, let the phone complete one full charge at standard rate without interrupting it. On the next charge cycle, fast charge should negotiate normally — confirm by checking that the phone reports fast charging within the first few minutes of plugging in.