LG KU198 Replacement Battery 3.7V 550mAh Li-ion

LG KU198 — 3.7V Li-ion Replacement Battery

This is a 3.7V, 550mAh Li-ion replacement battery for the LG KU198 candybar mobile phone. It slots directly into the KU198's battery bay and reconnects the phone to normal operation after the original cell has degraded. Voltage and capacity match the OEM spec: 3.7V, 550mAh (2.04Wh).

• KU198 compatibility: The KU198 runs a simple 3.7V single-cell Li-ion power rail with no advanced BMS handshake. The phone's charge IC reads cell voltage directly, so any correctly specced 3.7V Li-ion cell with a matching connector will be accepted by the device without a communication protocol barrier.
• Bench tested on actual hardware: We ran charge and discharge cycles through the KU198's onboard charge IC. The BMS accepted the cell without rejection, charge termination triggered correctly at 4.2V, and the cutoff fired at the expected low-voltage threshold without a hard lockout event.
• Fuel gauge recalibration after cell swap: On first use after installing this cell, run one full discharge down to auto-shutdown, then charge uninterrupted to 100%. The KU198's fuel gauge IC was calibrated against the original cell's discharge curve — one complete cycle resets the reference point and eliminates erratic percentage readings from the start.

Why the KU198 reports wrong battery percentage after a cell swap

The KU198 uses a coulomb-counting fuel gauge IC that tracks charge by measuring current in and out over time. When the original cell degrades, the IC adjusts its internal model to match the degraded curve. A fresh 550mAh cell has a steeper, higher-voltage discharge profile than a worn cell. Until the IC runs one full reference cycle on the new cell, it will misread state-of-charge — often showing 100% prematurely or jumping in large steps. One uninterrupted discharge-to-shutdown followed by a full charge corrects the calibration.

Sudden shutdown at 15–25% on the replacement cell

This happens when the phone's screen backlight or network radio pulls a brief current spike that drops cell voltage below the protection threshold. On a new cell with an uncalibrated fuel gauge, the phone may show 20% remaining while the actual resting voltage is already near 3.5V under load. The protection circuit reads the sag as an undervoltage event and cuts output before the display percentage reaches zero. Let the phone complete two full discharge-charge cycles — by the second cycle, the fuel gauge IC tracks load voltage more accurately and the early shutdowns stop.