{"product_id":"verizon-vs840-replacement-battery-37v-1200mah-li-ion","title":"BL-44JS Verizon VS840 Replacement Battery 3.7V 1200mAh","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eVerizon VS840 Lucid Series — 3.7V Li-ion Replacement Battery (BL-44JS)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThis is a 3.7V, 1200mAh Li-ion cell built to replace the OEM BL-44JS battery in the Verizon VS840, Lucid, Para, and Cayman smartphones. It fits the same footprint at 65.00 × 43.80 × 4.50mm and connects to the stock charge IC without modification. Swap it in when the original cell no longer holds a usable charge through a normal day.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003eVS840 \/ Lucid platform fit:\u003c\/strong\u003e\n    The VS840, Lucid, Para, and Cayman share the same battery bay dimensions and connector pinout, which is why BL-44JS crosses all of them. The BMS communicates over the same thermistor line, so the charge IC recognises the new cell without triggering a fault.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eBench tested on actual hardware:\u003c\/strong\u003e\n    We cycled this cell through the VS840's charge IC at the stock 500mA input rate. The BMS held cutoff correctly at 4.2V charge termination and 3.0V low-voltage cutoff, with no thermal events across three full cycles.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eFuel gauge recalibration on first use:\u003c\/strong\u003e\n    On first installation, disable fast charging if available and let the phone complete one full discharge down to auto-shutdown, then charge uninterrupted to 100%. The VS840's fuel gauge IC maps its coulomb counter to the new cell's discharge curve during this cycle — skipping it causes the percentage readout to drift immediately.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\n  \u003chr class=\"bpw-desc-divider\"\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eWhy the VS840 reports wrong battery percentage after a cell swap\u003c\/h3\u003e\n\n  \u003cp class=\"bpw-desc-p\"\u003eThe VS840 uses a fuel gauge IC that stores a learned discharge curve from the original cell. When you install a new cell, that stored curve no longer matches the actual voltage-to-capacity relationship of the replacement. The gauge reads voltage correctly but maps it against the wrong curve, so it can show 40% when the cell is near cutoff. One complete discharge-to-shutdown followed by an uninterrupted charge to 4.2V forces the IC to rewrite its learned table against the new cell. After that cycle, percentage accuracy normalises.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eSudden shutdown at 20–30% on the replacement cell\u003c\/h3\u003e\n\n  \u003cp class=\"bpw-desc-p\"\u003eThis happens when the modem or screen draws a current spike the cell cannot sustain at its present state of charge — voltage drops below the BMS cutoff threshold even though the gauge still shows capacity remaining. It is a voltage cliff, not a capacity defect. The fuel gauge IC hasn't yet calibrated where that cliff sits on the new cell's curve. Run one full discharge cycle without interruption and the gauge IC shifts its low-voltage warning threshold to match the actual cutoff point — typically resolving shutdowns above 3.2V per cell.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43405021151322,"sku":"BWCS-LVS840SL-1","price":23.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43405021184090,"sku":"BWCS-LVS840SL-2","price":26.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43405021216858,"sku":"BWCS-LVS840SL-3","price":29.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-LVS840SL-1.webp?v=1779369841","url":"https:\/\/batteryweb.com\/products\/verizon-vs840-replacement-battery-37v-1200mah-li-ion","provider":"BatteryWeb","version":"1.0","type":"link"}