QMobile Z8 Plus 3.8V Replacement Battery 3000mAh Li-Polymer

QMobile Z8 Plus — 3.8V Li-Polymer Replacement Battery (C866640282L)

This 3.8V, 3000mAh Li-Polymer battery replaces part number C866640282L in the QMobile Z8 Plus smartphone. It matches the original cell's voltage, capacity, and connector configuration. Dimensions are 86.60 × 65.90 × 4.00mm — verify against your existing cell before installing.

• Z8 Plus cell compatibility: The Z8 Plus uses a Li-Polymer pouch cell with a specific BMS handshake tied to the phone's charge IC. This replacement carries the same voltage rating and connector pinout, so the charge circuit recognises it without triggering a protection fault on first boot.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a controlled bench rig. The BMS held the 4.35V upper cutoff correctly and did not trip the protection circuit under simulated modem and screen load.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard current. This gives the fuel gauge IC time to map its coulomb counter against the new cell's discharge curve before high-current charging begins on an uncalibrated cell.

Sudden shutdown at 20–30% on the Z8 Plus after a cell swap

A new cell has a different internal resistance profile than the aged cell the fuel gauge IC was calibrated against. Under heavy load — active LTE, screen at full brightness, GPS — the cell voltage drops sharply. The phone's protection circuit reads this as a critically low voltage event and cuts power, even though the reported percentage looks safe. One full discharge-charge cycle resets the coulomb counter and tightens the percentage-to-voltage mapping. After calibration, the shutdowns typically stop.

USB fast charge not activating on the first cycle after replacement

The Z8 Plus charge IC negotiates fast charge protocols with the BMS on the cell. A new BMS may not complete this handshake successfully on the first charge cycle, causing the phone to fall back to standard 5V charging. This is not a fault with the battery or the charger. Fully discharge the phone, then plug in using the original cable and charger — on the second or third cycle the handshake completes and fast charge activates normally at the expected input voltage.