CAT S61 APP00262 Replacement Battery 3.8V 4000mAh

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

This 3.8V 4000mAh Li-Polymer battery replaces the original APP00262 cell in the CAT S61 rugged smartphone. It fits the S61 directly and matches the original voltage, capacity, and connector. At 15.2Wh, it restores the power the S61 needs to run its thermal camera, air quality sensor, and LTE modem under load.

• CAT S61 fit: The S61 runs a sealed unibody chassis with a dedicated Li-Polymer bay. The APP00262 cell matches the original BMS handshake, connector pinout, and 69.70 × 61.00 × 6.80mm form factor — no flex cable rerouting required.
• Bench tested on actual hardware: We cycled this cell through full discharge and charge under sustained screen-on and modem load. The BMS held voltage within spec across the discharge curve and engaged cutoff correctly at the low-voltage threshold.
• Fuel gauge recalibration on first use: Disable fast charging for the first complete discharge-charge cycle after installation. The S61's fuel gauge IC is calibrated to the old cell's discharge curve — one slow cycle lets it remap against the new cell before high-current charging begins.

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

This is a voltage cliff, not a capacity fault. The S61's Qualcomm modem, thermal camera module, and display draw simultaneous current spikes that pull cell voltage below the BMS cutoff threshold — even when the fuel gauge still reads 20–30%. It happens because the coulomb counter inherited state-of-charge data from the previous cell and has not yet mapped the new cell's actual voltage-to-capacity curve. Run one full discharge to near-zero, then charge uninterrupted to 100%. After that cycle the fuel gauge IC recalibrates and the shutdowns stop.

CAT S61 not powering on after sitting in storage

Li-Polymer cells self-discharge during storage. If the cell drops below 2.5V per cell, the BMS enters lockout mode and blocks all charge current to prevent thermal runaway on an over-discharged cell. The S61 will show no charge indicator and will not respond to the power button. Connect it to a wall charger — not a USB port — and leave it for 20–30 minutes. Most BMS controllers will accept a trickle recovery charge once input voltage is detected; the screen will eventually show the charging indicator and normal boot becomes possible once the cell climbs above 3.0V.