{"product_id":"xiaomi-mi-mix-replacement-battery-385v-4000mah-li-polymer","title":"Xiaomi Mi Mix BM4C Replacement Battery 3.85V 4000mAh","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eXiaomi Mi Mix Series — 3.85V Li-Polymer Replacement Battery (BM4C)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThe BM4C is a 3.85V, 4000mAh (15.4Wh) Li-Polymer cell that fits the Xiaomi Mi Mix, Mi Mix Dual SIM, Mi Mix Exclusive, and Mi Mix Exclusive Gold Ceramic Edition. It replaces a degraded or failed original cell to restore full display, processor, and modem power. Dimensions are 76.74 × 72.10 × 4.46mm — confirm your original cell matches before installing.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003eMi Mix variant coverage:\u003c\/strong\u003e\n    All listed Mi Mix variants share the same chassis footprint, connector pinout, and BMS handshake protocol — one cell fits all four. The BM4C part number is the key identifier across every variant, including the Gold Ceramic Edition.\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 cycles on Mi Mix hardware and confirmed BMS communication, charge IC acceptance, and voltage regulation across low-load and high-draw states. The cell held stable output under simultaneous display and modem load.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eFirst-cycle calibration tip:\u003c\/strong\u003e\n    On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate against the new cell's discharge curve before high-current fast charging pushes current into 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\"\u003eWhy the Mi Mix reports wrong battery percentage after a cell swap\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eThe Mi Mix uses a coulomb counter in the fuel gauge IC that builds a discharge model from cycle history. When you swap the physical cell, that stored model no longer matches the new cell's actual voltage-to-capacity curve. The IC keeps reporting percentages based on the old cell's behaviour, so readings appear inflated or deflated by 10–20%. One full discharge down to automatic shutdown followed by an uninterrupted charge to 100% forces the IC to rebuild its reference curve against the new cell.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eSudden shutdown at 20–30% remaining on the replacement cell\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eThis happens when the fuel gauge IC is still calibrated to an aged cell with a shallow, flat discharge curve. The new cell has a steeper voltage drop under modem or screen load, so the actual cell voltage hits the BMS cutoff threshold — typically around 3.0V — well before the reported percentage reaches zero. The phone cuts out because the cell voltage is genuinely too low, not because of a hardware fault. Run two full discharge-to-shutdown cycles without fast charging and the reported percentage will track the actual cell voltage correctly.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43392088342618,"sku":"BWCS-MUM440XL-1","price":25.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43392088375386,"sku":"BWCS-MUM440XL-2","price":28.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43392088408154,"sku":"BWCS-MUM440XL-3","price":31.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-MUM440XL-1.webp?v=1779143685","url":"https:\/\/batteryweb.com\/products\/xiaomi-mi-mix-replacement-battery-385v-4000mah-li-polymer","provider":"BatteryWeb","version":"1.0","type":"link"}