UMX AB043446LA Samsung SGH-T619 Replacement Battery 3.7V 750mAh

UMX MXC-550 — 3.7V Li-ion Replacement Battery (AB043446LA)

This 3.7V, 750mAh Li-ion battery replaces the AB043446LA cell in the UMX MXC-550 mobile phone. It fits the original battery bay and connector without modification. Voltage and capacity match the factory specification exactly.

• MXC-550 fit: The MXC-550 uses a single-cell Li-ion pack with a compact footprint — 49.53 × 33.73 × 7.29mm. The AB043446LA part number is the only cell that clears the battery bay depth and mates with the phone's three-pin connector without forcing the back cover.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the MXC-550 platform. The BMS accepted charge handshake on first connection, reached 4.2V at full charge, and held the low-voltage cutoff at 3.0V without triggering premature shutdown under screen and modem load.
• Fuel gauge recalibration after install: On first use, disable any fast-charge accessory and run one complete discharge-to-charge cycle at standard current. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current charging pushes current into an uncalibrated state.

Why the MXC-550 reports wrong battery percentage after a cell swap

The MXC-550 uses a fuel gauge IC that tracks charge state by learning the cell's discharge curve over repeated cycles. When a new cell goes in, the IC is still calibrated to the old, degraded cell — so its percentage readings are inaccurate from the start. The phone may show 40% remaining and cut off moments later, or sit at 100% far longer than expected. One full discharge down to auto-shutdown followed by a complete charge resets the coulomb counter and brings percentage reporting back in line.

Sudden shutdown at 20–30% on the replacement cell

This happens when the modem or display draws a brief high-current spike and the cell voltage dips below the BMS cutoff threshold — even though the fuel gauge still shows charge remaining. It is a calibration gap, not a defective cell. The fuel gauge IC has not yet learned the new cell's voltage cliff. Run two full discharge-charge cycles at standard current, and the shutdowns should stop. If the phone still cuts out after two cycles, check that resting cell voltage reads at least 3.7V with a multimeter before reinstalling.