Coolpad 8070D Replacement Battery CPLD-109 3.7V 1400mAh

Coolpad 8070D — 3.7V Li-ion Replacement Battery (CPLD-109)

This is a 3.7V, 1400mAh Li-ion cell built to fit the Coolpad 8070D smartphone. It replaces part number CPLD-109 — the original internal battery that powers calling, messaging, and app functions. When the original cell degrades and can no longer hold adequate charge, this replacement restores full device operation.

• Coolpad 8070D fit: The 8070D uses a fixed connector pinout and cavity measuring 55.81 × 50.83 × 5.25 mm. This cell matches that footprint and wiring directly. The BMS protection circuit communicates correctly with the phone's charge IC without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the 8070D platform. The BMS held charge termination correctly and did not trip on normal screen or modem loads. Voltage under load stayed within the expected range for a 3.7V nominal cell.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging begins. Skipping this step causes erratic percentage readings in the first few days of use.

Why the 8070D reports wrong battery percentage after a cell swap

The 8070D uses a fuel gauge IC that stores a learned discharge curve from the original cell. When a new cell goes in, the IC is still reading against the old curve. The percentage displayed reflects the old cell's behaviour, not the new cell's actual state of charge. One full discharge to automatic shutdown followed by an uninterrupted charge to 100% resets the coulomb counter and syncs the gauge to the new cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops sharply under the combined load of the modem radio and display — a voltage cliff the fuel gauge did not predict. The phone shuts down not because the percentage is low, but because instantaneous voltage fell below the protection threshold. Check the resting voltage after shutdown — if it recovers above 3.6V within a few minutes, the cell is intact and the gauge is uncalibrated. Run one full cycle from shutdown to 100% charge to correct it.