ZTE Z820 Li3818T43P3h635450 Compatible Battery 3.8V 1800mAh

ZTE Z820 Obsidian — 3.8V Li-ion Replacement Battery (Li3818T43P3h635450)

This is a 3.8V, 1800mAh Li-ion replacement battery for the ZTE Z820 Obsidian smartphone. It fits the Z820 directly and restores power when the original cell has degraded past usable capacity. Voltage and form factor match the OEM spec: 62.90 × 53.95 × 5.00mm.

• Z820 and Obsidian compatibility: Both names refer to the same hardware platform. The Z820 and Obsidian share identical connector pinout, BMS handshake requirements, and the same 3.8V nominal rail — this cell meets all three.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Z820 platform. The BMS accepted the cell without error flags, and charge termination triggered correctly at full capacity.
• First-cycle fast charge advice: On first use after installation, disable fast charging and complete one full discharge-charge cycle. This lets the phone's fuel gauge IC recalibrate against the new cell's discharge curve before high-current charging pushes current into an uncalibrated cell.

Why the Z820 reports wrong battery percentage after a cell swap

The Z820 uses a fuel gauge IC that builds its charge model from the original cell's discharge curve over time. When you install a new cell, that model no longer matches the actual cell chemistry. The IC may report 100% when the cell is not full, or drop percentage faster than expected. One complete discharge-charge cycle — from above 5% down to automatic shutdown, then a full uninterrupted charge — resets the coulomb counter against the new cell and corrects the readout.

Sudden shutdown at 20–30% on the Z820 after replacement

This is a voltage cliff issue, not a capacity defect. When the modem transmits or the screen brightness spikes, current draw jumps sharply. If the fuel gauge IC is still calibrated to the old cell's internal resistance curve, it misreads the voltage sag and triggers a low-voltage shutdown before the cell is actually depleted. The fix is the same full calibration cycle — discharge the phone naturally to automatic shutdown, then charge to 100% without interruption. After one cycle, the IC maps the new cell's voltage behaviour under load and the premature shutdowns stop.