About this replacement
LG X440 / W30 Plus — 3.85V Li-Polymer Replacement Battery (LG4000STCL02)
This is a 3.85V, 3900mAh Li-Polymer cell replacing OEM part LG4000STCL02. It fits the LG X440, LMX440IM, W30 Plus, and W30 2019 smartphones. The cell dimensions are 87.40 × 66.70 × 3.80mm — verify your original before installing.
- X440 and W30 series compatibility: These models share the same battery footprint, connector pinout, and BMS handshake protocol. The fuel gauge IC on each device reads the same coulomb counter registers, so the same cell works across all listed variants without firmware conflicts.
- Bench tested on actual hardware: We cycled this cell on an LMX440IM under mixed screen-on and modem-active load. The BMS held the protection threshold correctly and did not trigger false undervoltage cutoff during the first three cycles.
- Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard rate. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging begins on an uncalibrated cell.
Sudden shutdown at 20–30% on the replacement cell
This is a voltage cliff issue, not a capacity fault. Under peak modem or display load, a fresh cell with an uncalibrated fuel gauge can sag below the BMS protection threshold before the OS reads 0%. The phone shuts down because the BMS trips, even though the percentage indicator still shows charge remaining. One full discharge-charge cycle at standard rate realigns the coulomb counter to the new cell's actual voltage curve. After that cycle, shutdowns at 20–30% should stop — if they continue, verify cell voltage under load sits above 3.4V mid-discharge.
OS reporting wrong battery percentage after cell swap
The fuel gauge IC stores a learned discharge model from the original cell. After a swap, it applies that old curve to the new cell, producing percentage readings that jump, stall, or report full charge too early. The fix is a single full discharge to approximately 3.0V followed by an uninterrupted charge to 100% at standard rate — no fast charging during this cycle. That forces the coulomb counter to rewrite its reference table against the new cell. Most LG devices recalibrate within one cycle; erratic readings that persist past two cycles usually indicate a firmware battery stats reset is also needed in the device's service menu.