{"product_id":"cat-s31-replacement-battery-385v-3900mah-li-polymer","title":"CAT S31 Smartphone Replacement Battery APP00240 3.85V 3900mAh","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eCAT S31 — 3.85V Li-Polymer Replacement Battery (APP00240)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThis 3.85V, 3900mAh Li-Polymer cell replaces the original APP00240 battery in the CAT S31 rugged smartphone. It fits the S31 directly — same connector, same BMS handshake, same physical footprint at 95.60 × 54.22 × 4.40mm. Capacity figure is taken from the product specification, not estimated.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003eCAT S31 compatibility:\u003c\/strong\u003e\n    The S31 uses a sealed chassis with a fixed connector pinout tied to a specific BMS communication protocol. This cell matches that pinout and negotiates correctly with the S31's charge IC — no adapter, no firmware workaround needed.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eBench tested on actual hardware:\u003c\/strong\u003e\n    We ran the APP00240 replacement through full charge cycles on the S31 platform. The BMS accepted the cell without fault flags, charge current ramped normally through CC\/CV phases, and the fuel gauge IC registered capacity without throwing calibration errors on the first full cycle.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eFuel gauge recalibration after installation:\u003c\/strong\u003e\n    On first use, disable fast charging and run one complete discharge-to-charge cycle at standard current. 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.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\n  \u003chr class=\"bpw-desc-divider\"\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eSudden shutdown at 20–30% on the CAT S31 after a cell swap\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eThe S31's fuel gauge IC retains the discharge curve from the old, degraded cell in its coulomb counter. When a new cell is installed, the gauge reports percentage against that old curve — which means the displayed percentage no longer matches the actual cell voltage. Under modem transmit load or screen-on draw, the new cell hits a voltage cliff the gauge didn't predict, and the phone cuts out. One full discharge-to-shutdown followed by an uninterrupted charge to 100% forces a recalibration cycle. After that cycle, the percentage readings align with the new cell's actual state of charge.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eUSB charging not initiating after deep discharge storage\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eIf the replacement cell sat in storage at low voltage, the BMS protection circuit can lock out below approximately 2.5V per cell — the USB port will show no charge activity at all when connected. The fix is a trickle pre-charge: use the original CAT wall adapter rather than a PC USB port, which delivers enough idle current to nudge the cell above the BMS recovery threshold. Hold the cable connected for 10–15 minutes before attempting a power-on. Once cell voltage clears 3.0V, the BMS releases the lockout and normal CC\/CV charging resumes.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43391996723290,"sku":"BWCS-CAS310SL-1","price":27.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43391996756058,"sku":"BWCS-CAS310SL-2","price":31.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43391996788826,"sku":"BWCS-CAS310SL-3","price":34.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-CAS310SL_1.webp?v=1779142855","url":"https:\/\/batteryweb.com\/products\/cat-s31-replacement-battery-385v-3900mah-li-polymer","provider":"BatteryWeb","version":"1.0","type":"link"}