AT&T Z998 Replacement Battery 3.8V 2000mAh Li-ion

AT&T Z998 — 3.8V Li-ion Replacement Battery

This is a 3.8V, 2000mAh Li-ion battery for the AT&T Z998 smartphone. It replaces the original cell when capacity has dropped, charging has become inconsistent, or the battery no longer holds a charge. Dimensions are 58.35 x 51.20 x 5.50mm — verify clearance before installation.

• Z998 cell match: The Z998 uses a single-cell Li-ion configuration at 3.8V nominal. This replacement matches that voltage rail exactly — the charge IC on the Z998 will reject cells outside its accepted input range, so voltage tolerance matters.
• Bench tested on actual hardware: We cycled this cell through charge and discharge under screen-on and modem-active loads. The BMS held cutoff correctly at the low-voltage threshold and did not trip during the high-current draw of LTE data bursts.
• Fuel gauge recalibration after install: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard rate. This lets the fuel gauge IC build an accurate discharge curve against the new cell before the charge IC pushes high current into an uncalibrated state.

Sudden shutdown at 20–30% on the Z998 after a cell swap

The Z998 fuel gauge IC retains the discharge curve of the old cell. When a new cell with different internal impedance goes in, the gauge misreads remaining capacity. Voltage drops faster than the IC expects under modem or screen load, and the device shuts off before the display reaches 0%. One full discharge-charge cycle at standard current rewrites the coulomb counter reference and corrects the cutoff point.

Device not powering on after the battery sat in storage

Li-ion cells in storage self-discharge over time. If the cell drops below approximately 2.5V, the BMS locks out to prevent damage — the phone will not respond to a power button press or show a charging indicator. Connect the Z998 to a wall adapter and leave it untouched for 15–30 minutes. The charge IC on the phone will trickle current into the cell until voltage clears the BMS lockout threshold, after which normal charging resumes.