AT&T Z922 Replacement Battery 3.7V 1200mAh Li-ion

AT&T Z922 / Avail II Series — 3.7V Li-ion Replacement Battery

This is a 3.7V, 1200mAh Li-ion battery for the AT&T Z922, Avail II, Avail II 3G, and Avail 2 smartphones. It fits directly into the original battery compartment and restores power when the factory cell has degraded past usable capacity. Capacity is 4.44Wh — matching the original cell specification.

• Z922 and Avail II platform fit: These four models share the same battery bay dimensions, voltage rail, and connector pinout. The cell footprint is 49.00 × 47.80 × 5.50 mm, which keeps the rear cover flush without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Z922 platform. The BMS accepted charge current normally and terminated at full voltage without fault codes. No thermal events occurred during the charge cycle.
• Fuel gauge recalibration on first use: On first use after installation, run one full discharge down to automatic shutdown, then charge uninterrupted to 100% before resuming normal use. This gives the fuel gauge IC a complete reference curve for the new cell — skipping this step is the main reason percentage readings jump erratically in the first few days.

Sudden shutdown at 20–30% on the Z922 after a cell swap

A new Li-ion cell has a slightly different discharge curve than the aged cell the fuel gauge IC was calibrated against. At high load — mobile data, screen at full brightness, GPS — the Z922's modem draws a current spike the new cell cannot sustain at that state of charge without voltage sagging below the cutoff threshold. The phone interprets this as a dead battery and shuts down, even though the coulomb counter still shows charge remaining. One full discharge-charge cycle resets the IC's reference points and eliminates most of these early shutdowns.

Phone warm near the battery bay during the first charge cycle

A fresh Li-ion cell starts with higher internal impedance than a broken-in cell. The charge IC pushes current into higher resistance, and that resistance dissipates as heat. This is normal on the first one or two cycles and reduces as the cell breaks in. If warmth persists past the third full charge, check that the rear cover is fully seated — a partially open cover traps heat against the battery bay. Surface temperature above 45°C on the back panel is the threshold to stop charging and inspect.