ZOPO S5570 Replacement Battery BT557S 3.8V 3000mAh

ZOPO S5570 / Speed 7 Plus — 3.8V Li-Polymer Replacement Battery (BT557S)

This is a 3000mAh, 3.8V Li-Polymer battery for the ZOPO S5570 and Speed 7 Plus smartphones. It replaces OEM part BT557S when the original cell has degraded or stopped holding charge. Capacity is 11.4Wh at the rated voltage.

• S5570 and Speed 7 Plus compatibility: Both models share the BT557S connector pinout and the same BMS handshake protocol, so one cell fits either device without modification to the charge circuit.
• Bench tested on actual hardware: We cycled the BT557S through full charge and load discharge on the Speed 7 Plus platform. The BMS held charge termination correctly and did not trigger overcurrent cutoff during screen-on modem load.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging and run one complete discharge-charge cycle at standard rate. The fuel gauge IC in these phones calibrates its coulomb counter to the new cell's discharge curve — skipping this step causes erratic percentage readings for the first several cycles.

Sudden shutdown at 20–30% on the ZOPO S5570

The S5570 shuts down in the 20–30% range when the cell can no longer sustain voltage under combined modem and display load. A worn cell hits a voltage cliff — its open-circuit voltage looks acceptable, but under draw it collapses below the BMS cutoff threshold. A fresh BT557S cell holds above that threshold across the same load. After fitting the replacement, run one full discharge cycle before trusting the percentage readout — the fuel gauge needs to map the new cell's curve before it reports accurately under load.

Phone warm near the battery compartment on first charge after swap

A new Li-Polymer cell arrives with higher internal impedance than a broken-in cell. On the first charge cycle, the charge IC pushes current into that higher-impedance cell, which converts more energy to heat than usual. This is normal for the first one or two cycles and reduces as the cell breaks in. If warmth persists beyond the second full charge, check that the charge IC is not running a fast-charge profile — revert to standard 5V charging until the fuel gauge IC completes its first full calibration cycle.