{"product_id":"infinix-hot-4-pro-replacement-battery-385v-3900mah-li-polymer","title":"Infinix Hot 4 Pro BL-39AX Replacement Battery 3.85V 3900mAh","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eInfinix Hot 4 Pro \/ X556 \/ X5511 — 3.85V Li-Polymer Replacement Battery (BL-39AX)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThis is a 3900mAh Li-Polymer cell rated at 3.85V, replacing the original BL-39AX battery in the Infinix Hot 4 Pro, X556, and X5511. It fits the original battery compartment at 89.50 × 63.35 × 4.70mm. Swap it in when the original cell can no longer hold a usable charge across a full day.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003eHot 4 Pro \/ X556 \/ X5511 fitment:\u003c\/strong\u003e\n    All three model numbers share the same PCB layout, connector pinout, and BMS handshake protocol. One cell covers all three — no adapter or wiring change required.\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 the X556 platform. The BMS accepted the cell without fault codes, and the charge IC reached termination voltage at the correct 4.35V cutoff.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eFuel gauge recalibration on first cycle:\u003c\/strong\u003e\n    On first use after installation, disable fast charging and run one full discharge down to automatic shutdown, then charge to 100% uninterrupted. This lets the fuel gauge IC map the new cell's discharge curve before the coulomb counter locks in its reference points.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\n  \u003chr class=\"bpw-desc-divider\"\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eWhy the Hot 4 Pro reports wrong battery percentage after a cell swap\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eThe fuel gauge IC on this platform stores a learned discharge curve from the original cell. When a new cell goes in, the IC is still referencing old impedance and capacity data. Until it runs at least one full cycle, the percentage readout can be off by 10–20%. A single uninterrupted discharge-to-shutdown followed by a full charge resets the coulomb counter and brings percentage reporting back into alignment with the new cell's actual characteristics.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eSudden shutdown at 20–30% charge remaining on the replacement cell\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eThis is a voltage cliff issue, not a capacity fault. Under modem transmission load or peak screen brightness, the cell voltage drops sharply below the BMS cutoff threshold — even when the reported percentage still looks healthy. The fuel gauge IC hasn't finished calibrating, so it doesn't predict the voltage drop correctly. Run two full discharge-charge cycles and the IC will tighten its model; if shutdowns persist past that point, check that the battery connector is fully seated and making clean contact on all four pads.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43391988236378,"sku":"BWCS-FNX556SL-1","price":30.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43391988269146,"sku":"BWCS-FNX556SL-2","price":34.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43391988301914,"sku":"BWCS-FNX556SL-3","price":37.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-FNX556SL-1.webp?v=1779142762","url":"https:\/\/batteryweb.com\/products\/infinix-hot-4-pro-replacement-battery-385v-3900mah-li-polymer","provider":"BatteryWeb","version":"1.0","type":"link"}