{"product_id":"redmi-k40-5g-replacement-battery-387v-4400mah-li-polymer","title":"Redmi K40 5G Compatible Battery 3.87V 4400mAh Li-Polymer","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eRedmi K40 5G \/ K40 Pro 5G \/ K40 Pro+ 5G — 3.87V Li-Polymer Replacement Battery\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThis 3.87V, 4400mAh Li-Polymer cell replaces the original battery in the Redmi K40 5G, K40 Pro 5G, K40 Pro+ 5G, and M2012K11Q variants. It restores full power to the processor, display, modem, and all onboard systems. Dimensions are 87.00 x 64.20 x 4.30mm — physically identical to the factory cell.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003eK40 series platform fit:\u003c\/strong\u003e\n    The K40, K40 Pro, and K40 Pro+ share the same physical battery bay, connector pinout, and BMS handshake protocol. One cell fits all listed variants without modification.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eBench tested on actual hardware:\u003c\/strong\u003e\n    We ran this cell through full charge and discharge cycles on K40 hardware. The BMS accepted the cell on first contact, and charge IC communication registered correctly at 3.87V nominal without faults.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eFuel gauge recalibration on first use:\u003c\/strong\u003e\n    On first use after installation, disable fast charging for one complete discharge-charge cycle. 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 reference.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\n  \u003chr class=\"bpw-desc-divider\"\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eWhy the K40 reports wrong battery percentage after a cell swap\u003c\/h3\u003e\n\n  \u003cp class=\"bpw-desc-p\"\u003eThe K40's fuel gauge IC stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches actual voltage behaviour. The gauge reads a voltage, compares it to the old model, and outputs an incorrect percentage. One full slow-charge cycle — charge from flat to 100% without fast charge enabled — forces the coulomb counter to rebuild its reference map against the new cell's real chemistry.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eSudden shutdown at 20–30% on the replacement cell\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eThis happens when the fuel gauge IC is still running the old cell's voltage-to-capacity curve. The new cell hits a voltage cliff — typically around 3.50–3.55V — that the OS doesn't recognise as low, so no warning fires before the phone shuts down. It is not a defective cell. Run one full slow discharge-charge cycle, and the gauge recalibrates its low-voltage cutoff threshold to match the new cell. After that cycle, shutdowns below 20% should stop.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43391888654426,"sku":"BWCS-MUK400SL-1","price":28.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43391888687194,"sku":"BWCS-MUK400SL-2","price":32.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43391888719962,"sku":"BWCS-MUK400SL-3","price":35.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-MUK400SL-1.webp?v=1779142541","url":"https:\/\/batteryweb.com\/products\/redmi-k40-5g-replacement-battery-387v-4400mah-li-polymer","provider":"BatteryWeb","version":"1.0","type":"link"}