LG LS840 Replacement Battery BL-44JS 3.7V 2400mAh

LG LS840 — 3.7V Li-ion Replacement Battery (BL-44JS)

This is a 3.7V, 2400mAh Li-ion cell that replaces the original BL-44JS battery in the LG LS840 smartphone. It slots into the same battery bay and uses the same connector and contact layout as the factory unit. Voltage and capacity match the original spec exactly.

• LS840 fit confirmation: The LS840 uses a removable Li-ion pack with a three-contact terminal strip. This cell matches that contact layout, the physical footprint (64.90 × 43.70 × 10.60mm), and the 3.7V nominal voltage the phone's charge IC expects. No modifications needed.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS accepted charge current from the phone's onboard charge IC without tripping overcurrent protection, and the cell held voltage through a full discharge curve without premature cutoff.
• Fuel gauge recalibration after swap: On first use after installation, disable fast charging if available and run one complete discharge-charge cycle at standard rate. This gives the fuel gauge IC a clean reference curve against the new cell before any high-current charging pushes current into an uncalibrated cell.

Sudden shutdown at 20–30% on the LS840 after a cell swap

This is a voltage cliff issue, not a capacity defect. Under modem transmit load or display brightness peaks, the new cell's internal resistance causes a voltage dip the phone reads as critically low, triggering a hard shutdown. The fuel gauge IC is still calibrated to the old cell's discharge curve and doesn't know where the actual cutoff is on the new cell. One full discharge-charge cycle at standard rate forces the coulomb counter to rebuild its reference map. After that cycle, shutdowns at 20–30% stop in most cases.

LS840 not powering on after sitting in storage with a flat battery

If cell voltage drops below approximately 2.5V, the BMS enters a lockout state to prevent damage from over-discharge. The phone will show nothing when you press the power button — no logo, no charging animation. Connect the phone to a wall charger rather than a computer USB port, which may not supply enough current to wake the BMS. Leave it connected for 15–20 minutes; once the cell reaches around 3.0V, the BMS exits lockout and the phone will begin a normal charge cycle.