LG CU575 Replacement Battery 3.7V 980mAh Li-ion

LG CU575 / TU575 — 3.7V Li-ion Replacement Battery (LG-GBJM)

This is a 3.7V, 980mAh Li-ion cell built to the LG-GBJM spec, fitting the LG CU575, Trax CU575, and TU575 candybar handsets. These mid-2000s phones use a slim 70.40 × 46.80 × 5.40mm pack with a three-contact rear connector. Voltage and capacity match the original OEM cell exactly — no modifications needed to seat and run it.

• CU575, Trax CU575, and TU575 fit: All three models share the same battery bay dimensions, connector pinout, and 3.7V nominal voltage rail — one cell covers the full platform without adapter or trim.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a CU575 body. The BMS accepted charge from a standard 4.2V termination charger, held voltage above 3.6V through the mid-band of discharge, and tripped the low-voltage cutoff cleanly at the floor without hanging.
• Fuel gauge recalibration on first use: After fitting this cell, run one full discharge to automatic shutoff before recharging. The CU575 fuel gauge IC is calibrated to the old cell's discharge curve — one complete cycle lets it remap against the new cell and report accurate percentages from the second charge onward.

Why the CU575 reports wrong battery percentage after a cell swap

The CU575 uses a simple coulomb-counting fuel gauge IC that stores a learned discharge curve from the previous cell. When a new cell goes in, that stored curve no longer matches the actual voltage-versus-capacity slope of the replacement. The phone may show 40% remaining while the cell is near 3.5V, then drop to 5% without warning. One full discharge-to-cutoff followed by a full charge forces the IC to rebuild its reference map against the new cell. After that single cycle, the percentage readout tracks correctly.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff issue, not a capacity problem. Under the combined load of the GSM modem transmitting and the backlight active, the cell must sustain voltage above roughly 3.4V — if internal impedance is slightly higher than the original cell, voltage dips below the BMS cutoff threshold under that peak draw even when the coulomb count says 25% remains. The phone interprets this as a low-voltage fault and shuts down to protect the cell. Letting the fuel gauge recalibrate over one full cycle resolves most cases; if shutdowns persist, check that the battery contacts on the phone body are clean and making full metal-to-metal contact.