{"product_id":"xiaomi-mi-8-youth-replacement-battery-385v-3250mah-li-polymer","title":"Xiaomi Mi 8 Youth BM3J Replacement Battery 3.85V 3250mAh","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eXiaomi Mi 8 Youth — 3.85V Li-Polymer Replacement Battery (BM3J)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThis is a 3250mAh Li-Polymer cell at 3.85V, replacing part number BM3J in the Xiaomi Mi 8 Youth, Mi 8 Youth Standard Edition, Mi 8 Youth Standard Edition Dual SIM, and M1808D2TE. It fits when the original cell has degraded, swells, or no longer holds a usable charge. Voltage and capacity match the stock specification exactly.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003eMi 8 Youth platform fit:\u003c\/strong\u003e\n    The Mi 8 Youth, its Standard Edition, Dual SIM variant, and M1808D2TE all share the same battery bay geometry, connector pinout, and BM3J BMS handshake — the PMIC on this board checks cell identification on boot, so the part number must match to unlock fast charge signalling.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eBench tested on actual hardware:\u003c\/strong\u003e\n    We seated this cell in an Mi 8 Youth, ran the device through a full boot sequence, and confirmed the BMS negotiated correctly with MIUI's charge IC. Capacity readout at first boot landed within 2% of rated spec under a controlled load.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eFirst-cycle fuel gauge recalibration:\u003c\/strong\u003e\n    On first use after installation, disable fast charging and run one complete discharge-to-charge cycle. The fuel gauge IC was calibrated against the old cell's discharge curve — giving it one uninterrupted reference cycle before high-current charging prevents it from locking onto a skewed coulomb counter baseline.\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 Mi 8 Youth after a cell swap\u003c\/h3\u003e\n\n  \u003cp class=\"bpw-desc-p\"\u003eThis happens because the fuel gauge IC still holds the discharge curve of the old, degraded cell. The new cell has a steeper voltage cliff at low state-of-charge — the PMIC sees the rail drop below the cutoff threshold under modem or display load before the reported percentage reaches zero. The phone interprets this as a hard undervoltage event and shuts down to protect the system, even though the displayed percentage suggests charge remains. Running two full discharge-charge cycles without fast charging lets the coulomb counter re-anchor to the new cell's actual curve and eliminates most false shutdowns.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eUSB-PD or MIUI fast charge not activating after replacement\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eAfter a cell swap, some Mi 8 Youth units revert to standard 5V\/1A charging on the first cycle — the charge IC runs a handshake protocol on power-up that checks BMS response time, and a brand-new cell at partial state-of-charge can respond outside the expected window. This is not a fault with the charger or the cable. Fully discharge the phone to automatic shutdown, then connect the original fast charger from a cold boot. On the second or third full cycle, fast charge negotiation typically resumes at the correct voltage step.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43392016351322,"sku":"BWCS-MUM800SL-1","price":25.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43392016384090,"sku":"BWCS-MUM800SL-2","price":28.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43392016416858,"sku":"BWCS-MUM800SL-3","price":31.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-MUM800SL-1.webp?v=1779142904","url":"https:\/\/batteryweb.com\/products\/xiaomi-mi-8-youth-replacement-battery-385v-3250mah-li-polymer","provider":"BatteryWeb","version":"1.0","type":"link"}