About this replacement
LG K4 / K130 Series — 3.7V Li-ion Replacement Battery (BL-49JH)
This is a 3.7V, 1700mAh Li-ion cell built to replace the BL-49JH battery in the LG K4, K4 Dual SIM LTE, K130, K130E, and related variants. It slots into the same battery bay and connects to the same charge IC the original cell used. Capacity comes from the product specification — 6.29Wh total energy.
- K4 and K130 platform fit: These models share the same battery bay dimensions, connector pinout, and BMS communication protocol. A single 3.7V cell with matching thermistor and ID pin wiring covers the full variant range without adaptation.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on K130-series hardware. The BMS accepted the cell on first connection, charge current ramped correctly through CC/CV stages, and the protection circuit tripped at expected voltage limits under load.
- Fuel gauge recalibration on first cycle: After installing this battery, disable fast charging and run one full discharge-to-charge cycle before normal use. The fuel gauge IC on the K4 calibrates against the cell's discharge curve — skipping this step lets it push fast-charge current into an uncalibrated cell, which skews percentage readings from the first hour.
Sudden shutdown at 20–30% on the LG K4 after a cell swap
This happens because the fuel gauge IC is still tracking the old cell's voltage-to-capacity curve. The new cell hits a steeper voltage drop under modem or display load, and the phone's protection circuit shuts down before the reported percentage reaches zero. It is not a faulty battery — it is a calibration mismatch. Run two full discharge cycles without fast charging and the coulomb counter will remap to the new cell's actual curve.
Phone won't power on after the BL-49JH sat in storage
If the cell dropped below approximately 2.5V during storage, the BMS enters lockout mode and blocks charge current to prevent damage to a deeply discharged lithium cell. Standard wall charging will not wake it. Connect to a charger and leave it undisturbed for 20–30 minutes — the charge IC on the K4 delivers a low trickle current (around 100mA) to bring the cell back above the BMS re-enable threshold before switching to full charge current. If the phone still won't respond after 45 minutes on charge, check that the connector is fully seated on the battery terminal.