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

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

This is a 3.7V, 1200mAh Li-ion cell that fits the LG VS840, Lucid, Lucid 4G, and Cayman. It replaces OEM part numbers BL-44JS, EAC61838702, BL-A5JN, and EAC61680101. If your original cell has swollen, won't hold a charge, or the phone shuts down unpredictably, this is the direct swap.

• VS840 and Lucid platform fit: The VS840, Lucid, and Cayman share the same battery bay geometry, connector orientation, and voltage rail. All of these models accept the BL-44JS form factor without modification to the housing or contacts.
• Bench tested on actual hardware: We ran this cell through charge and load cycles on the VS840 platform. The BMS accepted the new cell without handshake errors, and the charge IC brought the cell up from a depleted state without triggering thermal cutoff.
• Fuel gauge recalibration on first cycle: After fitting this cell, run one full discharge down to automatic shutdown, then charge uninterrupted to 100% before using the phone heavily. This lets the VS840's fuel gauge IC map its coulomb counter to the new cell's actual discharge curve — skipping this step causes the percentage display to drift or jump in the first several days of use.

Why the VS840 reports the wrong battery percentage after a cell swap

The VS840's fuel gauge IC stores a charge profile calibrated to the original cell's internal resistance and capacity fade. When a new cell goes in, that stored profile no longer matches the actual discharge curve. The IC will over- or under-report state of charge until it re-learns the new cell. One full discharge-to-shutdown followed by an uninterrupted charge cycle resets the coulomb counter and forces a fresh calibration pass.

Sudden shutdown at 20–30% on the new cell

This happens when the modem or display draws a current spike and the cell voltage drops below the BMS cutoff threshold — even though the OS still shows 20–30% remaining. On the VS840, the fuel gauge hasn't yet mapped the voltage cliff of the new cell, so it doesn't warn the OS in time. The fix is the same calibration cycle: one complete drain to shutdown, then a full charge. After that cycle, the OS receives accurate low-battery warnings before the voltage cliff hits.