AT&T Galaxy S III Replacement Battery 3.7V 1400mAh

AT&T Galaxy S III — 3.7V Li-ion Replacement Battery

This is a 3.7V, 1400mAh Li-ion replacement battery for the AT&T Samsung Galaxy S III (Galaxy S3 / SIII). It fits the standard battery slot on these models and restores power to the display, processor, and wireless radios. Dimensions are 63.00 x 50.40 x 5.40mm — verify against your original cell before installing.

• Galaxy S III compatibility: The AT&T Galaxy S III, S3, and SIII variants all share the same battery bay dimensions, contact pin layout, and 3.7V nominal voltage rail. One replacement cell covers the full group.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on Galaxy S III hardware. The BMS accepted the charge IC handshake cleanly, and the protection circuit tripped correctly at low-voltage cutoff without nuisance trips during normal screen and modem load.
• Fuel gauge recalibration on first use: After installing this cell, disable fast charging and complete one full discharge-charge cycle before normal use. This gives the phone's fuel gauge IC time to map the new cell's discharge curve — without that cycle, the coulomb counter is still calibrated to the old, degraded cell and percentage readings will be unreliable.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff problem, not a capacity problem. Under high-current draw — LTE radio, screen-on navigation, or a GPU-intensive app — cell voltage drops sharply below what the fuel gauge IC predicted. The phone's protection circuit reads undervoltage and cuts power before the displayed percentage hits zero. One full discharge-charge cycle lets the fuel gauge IC relearn where the new cell's voltage actually collapses under load. After calibration, shutdowns at 20–30% typically stop.

Phone reports wrong battery percentage after cell swap

The Galaxy S III uses a coulomb counter that accumulates charge and discharge data over time. When you install a new cell, that counter still holds the curve from the old degraded battery. The mismatch causes the OS to display percentages that are 10–20% off real capacity — or to jump erratically between readings. Fix this by running one complete discharge down to auto-shutdown, then charging uninterrupted to 100%. That single cycle resets the fuel gauge IC against the actual capacity of the new cell.