Caterpillar S61 Replacement Battery 3.8V 4000mAh APP00262

CATERPILLAR S61 — 3.8V Li-Polymer Replacement Battery (APP00262)

This is a 3.8V, 4000mAh Li-Polymer battery for the CATERPILLAR S61 rugged smartphone. It replaces the original APP00262 cell when capacity has dropped or the battery no longer holds a usable charge. Voltage and chemistry match the original spec exactly.

• S61 platform fit: The S61 uses a dedicated battery bay with a connector keyed to the APP00262 footprint. The BMS handshake runs over the same contact pins as the original cell, so the phone's charge IC recognises the new battery without additional configuration.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the S61 platform. The BMS accepted the cell on first connection, charge termination triggered at the correct voltage, and the protection circuit cut off cleanly at the low-voltage threshold.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one full discharge-charge cycle at standard rate. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging begins on an uncalibrated cell.

Sudden shutdown at 20–30% on the S61 after a cell swap

The S61's fuel gauge IC stores a discharge curve from the previous cell. A new cell with a different internal impedance profile hits a voltage cliff earlier than the old calibration predicts. Under peak modem load or screen brightness, the cell voltage sags below the BMS cutoff threshold while the gauge still reads 20–30%. One full discharge cycle — draining to auto-shutdown and charging uninterrupted to 100% — resets the coulomb counter against the new cell and resolves the early cutoff.

USB fast charge not activating on the first cycle after replacement

Some S61 units negotiate fast charge through the charge IC, which checks cell impedance before stepping up current. A new cell at full impedance before its first cycle can cause the IC to fall back to standard 5V charging as a precaution. This is not a fault in the battery or charger. After the first complete charge cycle, impedance settles and the charge IC renegotiates the higher current tier on subsequent plugs.