{"product_id":"redmi-4-standard-edition-replacement-battery-385v-4000mah-li-polymer","title":"Redmi BN42 Smartphone Replacement Battery 3.85V 4000mAh","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eRedmi 4 Standard Edition — 3.85V Li-Polymer Replacement Battery (BN42)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThis is a 4000mAh Li-Polymer cell at 3.85V, replacing the original BN42 battery in the Redmi 4 Standard Edition. It fits the standard single-SIM and Dual SIM variants, including the TD-LTE model (2016090). Swap it in when the original cell no longer holds a charge or causes unexpected shutdowns.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003eCovers 4 Standard Edition variants:\u003c\/strong\u003e\n    The standard, Dual SIM, Dual SIM TD-LTE, and 2016090 board revision all use the same BN42 footprint, connector pinout, and BMS handshake. One cell fits all four without modification.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eBench tested on actual hardware:\u003c\/strong\u003e\n    We cycled this cell through charge and discharge on a Redmi 4 board. The BMS accepted the cell, thermal cutoff triggered correctly at high charge current, and the fuel gauge IC read within expected range after one full cycle.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eFuel gauge recalibration on first use:\u003c\/strong\u003e\n    On first install, disable fast charging and run one full discharge down to auto-off, then charge to 100% uninterrupted. This lets the fuel gauge IC map the new cell's discharge curve before it takes high-current input — skipping this step causes the percentage readout to drift for the first week.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\n  \u003chr class=\"bpw-desc-divider\"\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eWhy the Redmi 4 reports wrong battery percentage after a cell swap\u003c\/h3\u003e\n\n  \u003cp class=\"bpw-desc-p\"\u003eThe Redmi 4 uses a coulomb counter that builds its discharge model against the original cell's impedance curve. When a new cell goes in, that stored model no longer matches reality — especially in the 30–15% range where cell voltage drops steeply. The firmware keeps predicting remaining capacity based on old data, so the percentage reading lags or jumps. One complete discharge-charge cycle without interruption forces the fuel gauge IC to rebuild its reference curve against the new cell, and readings stabilise after that.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eSudden shutdown at 20–25% 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, screen, and CPU load, the cell voltage briefly dips below the BMS cutoff threshold — even though the fuel gauge still shows 20% or more remaining. Aged cells hit this cliff earlier because internal resistance rises, but a brand-new cell can trigger the same fault if the fuel gauge IC is uncalibrated and holds the phone active past the safe voltage floor. Run the recalibration cycle first; if shutdowns continue, check that the replacement cell voltage reads above 3.6V under load using a USB power meter or the built-in battery diagnostics at *#*#6485#*#*.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43392024248410,"sku":"BWCS-MUM414XL-1","price":25.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43392024281178,"sku":"BWCS-MUM414XL-2","price":28.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43392024313946,"sku":"BWCS-MUM414XL-3","price":31.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-MUM414XL-1.webp?v=1779142944","url":"https:\/\/batteryweb.com\/products\/redmi-4-standard-edition-replacement-battery-385v-4000mah-li-polymer","provider":"BatteryWeb","version":"1.0","type":"link"}