Allstar Z818L Replacement Battery 3.7V 1800mAh Li-ion

Allstar Z818L / Z818G (Straight Talk) — 3.7V Li-ion Replacement Battery

This is a 3.7V, 1800mAh Li-ion battery for the Allstar Z818L and Z818G smartphones sold through the Straight Talk network. It replaces the original cell when the phone no longer holds a charge or fails to power on. Capacity figure is 6.66Wh at rated voltage.

• Z818L and Z818G compatibility: Both models share the same battery bay dimensions (72.74 × 53.41 × 4.67mm), the same 3.7V nominal voltage rail, and an identical connector pinout — one cell fits both without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS accepted a standard 5V charge input without triggering over-voltage cutoff, and the protection circuit tripped correctly at the low-voltage threshold before cell damage occurred.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging and complete one full discharge-to-charge cycle before resuming normal use. The fuel gauge IC in the Z818L is calibrated to the old cell's discharge curve — skipping this step causes the phone to read incorrect percentages until the coulomb counter resets against the new cell.

Sudden shutdown at 20–30% on the Z818L after a cell swap

This is a voltage cliff issue, not a faulty battery. The Z818L's modem and screen together draw a current spike the fuel gauge IC maps incorrectly against the new cell's discharge curve. The phone's protection circuit reads a voltage sag as critically low and cuts power before the percentage counter reaches zero. One full discharge cycle — draining to automatic shutdown, then charging uninterrupted to 100% — lets the coulomb counter rebuild an accurate state-of-charge map. After that cycle, shutdowns at 20–30% stop.

Phone showing 1% or jumping percentage erratically after replacement

The fuel gauge IC stores learned capacity data from the original cell. When a new cell goes in, that stored data is wrong — the IC reports whatever the old curve predicted, not what the new cell is actually doing. Erratic jumps of 10–15% or a stuck reading near 1% are both symptoms of the same uncalibrated state. Charge the phone to 100% without interruption, use it until it shuts off automatically, then charge back to 100% in one session. That single full cycle forces the fuel gauge IC to recalculate against the new cell's actual discharge curve.