Zopo ZP780 Replacement Battery BT57S 3.7V 1800mAh Li-ion

ZOPO ZP780 / 6560 — 3.7V Li-ion Replacement Battery (BT57S)

This is a 3.7V, 1800mAh Li-ion cell built to replace the original BT57S battery in the ZOPO ZP780 and 6560 smartphones. It slots into the same battery bay and reconnects to the same charge IC and fuel gauge circuit. Capacity is rated at 6.66Wh.

• ZP780 and 6560 platform fit: Both devices share the same battery bay dimensions, connector pin-out, and charge IC handshake. The BT57S form factor — 77.15 × 59.85 × 3.70mm — is specific to this chassis. Fitting a cell outside those tolerances risks poor contact or case flex.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the ZP780 platform. The BMS accepted the cell without fault flags, the charge IC entered CC/CV mode correctly, and the fuel gauge IC began tracking state-of-charge within the first full cycle.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle. The fuel gauge IC carries calibration data from the old cell's discharge curve. Letting it map one full cycle against the new cell prevents erratic percentage readings from the first day.

Sudden shutdown at 20–30% on the ZP780 after a cell swap

This is a voltage-cliff issue, not a capacity fault. When the modem transmits or the screen brightness spikes, instantaneous current draw pulls the cell voltage below the BMS cutoff threshold — even when the fuel gauge still reports charge remaining. A new cell with an uncalibrated fuel gauge IC makes this worse, because the reported percentage does not match the cell's actual state of charge. Running one full discharge cycle from 100% to auto-off lets the coulomb counter reset its zero-point against the real cell capacity. After that cycle, shutdowns at falsely high percentages typically stop.

ZP780 not powering on after the battery sat in storage

Li-ion cells stored without charge self-discharge over weeks. If the cell drops below approximately 2.5V, the BMS enters lockout mode and blocks current flow to protect the cell from damage. The phone shows nothing on screen — no charge indicator, no vibration. Connect a known-good charger and leave it for 20–30 minutes without pressing the power button. The charge IC will trickle current into the cell until it clears the BMS recovery threshold, typically around 2.9–3.0V, after which normal charging resumes.