{"product_id":"xiaomi-mi-max-3-replacement-battery-385v-5400mah-li-polymer","title":"Xiaomi Mi Max 3 Replacement Battery BM51 5400mAh 3.85V","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eXiaomi Mi Max 3 — 3.85V Li-Polymer Replacement Battery (BM51)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThe BM51 is a 3.85V, 5400mAh Li-Polymer cell that fits the Xiaomi Mi Max 3, Mi Max 3 Dual SIM TD-LTE, M1804E4T, and M1804E4A. It replaces the original factory cell when the phone can no longer hold charge, shuts down unexpectedly, or fails to power on. Capacity is 20.79Wh — matching the original specification.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003eMi Max 3 platform fit:\u003c\/strong\u003e\n    All listed variants — M1804E4T, M1804E4A, single and dual SIM — use the same BM51 footprint, connector, and BMS communication protocol. The cell dimensions are 103.92 × 73.94 × 3.78mm, which match the original battery tray with no modification required.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eBench tested on actual hardware:\u003c\/strong\u003e\n    We ran the BM51 through charge and discharge cycles on Mi Max 3 hardware. The BMS accepted the cell without fault codes, and the charge IC cycled correctly through CC and CV phases at both standard and fast-charge current levels.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eFuel gauge recalibration on first use:\u003c\/strong\u003e\n    After installation, disable fast charging and run one complete discharge down to automatic shutdown, then charge uninterrupted to 100%. This gives the fuel gauge IC a full reference curve against the new cell before high-current charging begins.\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 Max 3 reports wrong battery percentage after a cell swap\u003c\/h3\u003e\n\n  \u003cp class=\"bpw-desc-p\"\u003eThe Mi Max 3 uses a coulomb counter that builds its charge curve against the old cell's impedance and capacity profile. When a new cell goes in, the counter still references the previous curve, so the percentage on screen drifts from the actual state of charge. This shows up as sudden jumps — the display may read 40% and then drop to 15% within a few minutes under load. One full uninterrupted discharge-to-shutdown followed by a complete charge cycle resets the reference and brings the display back into alignment.\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 is a voltage cliff issue, not a capacity problem. Under combined modem, display, and processor load, the cell voltage sags below the BMS cutoff threshold before the fuel gauge reaches 0%. It happens most often on the Mi Max 3's large screen when brightness is high and a data connection is active. The fix is the same recalibration cycle — one full discharge lets the fuel gauge IC map the actual voltage-to-capacity curve of the new cell. After calibration, the BMS cutoff and the displayed percentage stay in sync, and shutdowns below 3.2V under load stop occurring.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43392022773850,"sku":"BWCS-MUM180XL-1","price":26.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43392022806618,"sku":"BWCS-MUM180XL-2","price":30.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43392022839386,"sku":"BWCS-MUM180XL-3","price":33.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-MUM180XL-1.webp?v=1779142944","url":"https:\/\/batteryweb.com\/products\/xiaomi-mi-max-3-replacement-battery-385v-5400mah-li-polymer","provider":"BatteryWeb","version":"1.0","type":"link"}