Samsung SGH-T109 Replacement Battery AB043446LA 3.7V 750mAh

Samsung SGH-T109 / SGH-A237 Series — 3.7V Li-ion Replacement Battery (AB043446LABSTD)

This is a 3.7V, 750mAh Li-ion replacement battery for the Samsung SGH-T109 and a range of compatible SGH-series handsets including the SGH-M220, SGH-A227, and SGH-A237. It replaces OEM part AB043446LABSTD and AB043446LA. Capacity is 750mAh (2.78Wh), matching the original cell specification.

• SGH-series platform fit: The T109, M220, A227, and A237 all share the same 3.7V single-cell Li-ion bay, connector pinout, and BMS handshake protocol. One cell fits the entire group without modification.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on SGH-series hardware. The BMS accepted the cell without error, held charge termination at the correct voltage, and showed no thermal anomalies through three consecutive cycles.
• Fuel gauge recalibration on first install: After fitting this cell, run one complete discharge down to auto-shutoff and then charge uninterrupted to 100% before normal use. The SGH-series fuel gauge IC reads the new cell's discharge curve during that first full cycle — skipping it leaves the percentage counter misaligned with actual cell capacity.

Why the SGH-T109 shuts down suddenly at 20–30% remaining

The SGH-series fuel gauge IC stores a learned discharge curve from the original cell. When a new cell goes in, the IC still references the old curve, so it miscalculates the remaining usable voltage window. Under the transient load of an outgoing call or backlight burst, the new cell's actual voltage dips below the shutdown threshold before the gauge reaches 0%. One complete discharge-to-shutoff cycle forces the IC to relearn the curve against the replacement cell's actual characteristics, and the premature cutoffs stop.

Phone won't power on after the battery sat discharged in storage

Li-ion cells that drop below roughly 2.5V trip the BMS into a protection lockout state — the circuit opens to prevent damage to over-discharged cells. Plugging in a charger appears to do nothing because the phone's charge IC waits for a minimum voltage signal from the battery before starting the main charge stage. Connect the phone to a wall adapter (not a PC USB port, which may not supply enough current) and leave it for 15–20 minutes without pressing the power button. The charge IC trickle-charges the cell at low current until it clears the BMS lockout threshold, typically around 2.9V, at which point normal charging resumes and the phone will power on.