{"product_id":"redmi-7a-replacement-battery-385v-3900mah-li-polymer","title":"Redmi BN49 7A Replacement Battery 3.85V 3900mAh","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eRedmi 7A — 3.85V Li-Polymer Replacement Battery (BN49)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThe BN49 is the stock Li-Polymer cell for the Redmi 7A smartphone, covering model variants M1903C3EI, MZB7995IN, and MZB7798IN among others. It runs at 3.85V and carries 3900mAh (15.02Wh). This replacement restores power to the display, processor, and cellular radio when the original cell has degraded or failed.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003e7A variant compatibility:\u003c\/strong\u003e\n    All listed model numbers — M1903C3EI, MZB7995IN, MZB7798IN and the wider 7A regional variants — share the same chassis dimensions and connector pinout, so the BN49 fits without modification to the flex cable or adhesive frame.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eBench tested on actual hardware:\u003c\/strong\u003e\n    We cycled the BN49 through charge and discharge on the 7A platform, confirmed BMS handshake with the charge IC, and verified the protection circuit trips correctly at low-voltage cutoff without false positives during normal load.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eFuel gauge recalibration after swap:\u003c\/strong\u003e\n    On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard rate. This lets the fuel gauge IC map its coulomb counter against the new cell's discharge curve before any high-current charging session pushes current into an uncalibrated 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 Redmi 7A after a cell swap\u003c\/h3\u003e\n\n  \u003cp class=\"bpw-desc-p\"\u003eThis is a voltage-cliff problem, not a capacity problem. The fuel gauge IC still holds the old cell's discharge curve in memory, so its percentage reading no longer matches the new cell's actual voltage behaviour. When the modem transmits or the screen brightness spikes, current draw pulls the cell voltage below the system cutoff threshold — even though the gauge still shows 20–30%. One full slow-rate discharge-charge cycle forces the coulomb counter to re-anchor to the new cell's curve, and the shutdowns stop.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eRedmi 7A not powering on after the battery sat discharged in storage\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eIf the BN49 cell drops below approximately 2.5V during storage, the BMS enters lockout mode and blocks any charge current to prevent damage to an over-discharged cell. Plugging in a standard charger appears to do nothing — no charging LED, no boot. Connect the phone to a low-current USB source (a PC port rather than a wall adapter) and leave it for 15–20 minutes; the BMS trickle-recovery circuit will slowly raise cell voltage until it exits lockout. Once the LED shows any charge activity, switch to the wall adapter to complete the charge normally.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43392002359386,"sku":"BWCS-MUR700SL-1","price":25.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43392002392154,"sku":"BWCS-MUR700SL-2","price":28.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43392002424922,"sku":"BWCS-MUR700SL-3","price":31.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-MUR700SL-1.webp?v=1779142856","url":"https:\/\/batteryweb.com\/products\/redmi-7a-replacement-battery-385v-3900mah-li-polymer","provider":"BatteryWeb","version":"1.0","type":"link"}