BL-44JS Verizon VS840 Replacement Battery 3.7V 1200mAh

Verizon VS840 Lucid Series — 3.7V Li-ion Replacement Battery (BL-44JS)

This 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.

• VS840 / Lucid platform fit: 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.
• Bench tested on actual hardware: 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.
• Fuel gauge recalibration on first use: 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.

Why the VS840 reports wrong battery percentage after a cell swap

The 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.

Sudden shutdown at 20–30% on the replacement cell

This 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.