VIBO K520 Compatible Battery 3.7V 1000mAh Li-ion

VIBO K520 — 3.7V Li-ion Replacement Battery

This is a 3.7V, 1000mAh Li-ion battery for the VIBO K520 smartphone. It fits directly into the K520 and restores the phone's ability to hold a charge when the original cell has degraded. Capacity is 3.7Wh as shipped.

• K520 cell fit: The K520 uses a single-cell Li-ion pack at 3.7V nominal. This replacement matches the connector pinout and physical footprint — 53.00 × 33.90 × 5.70mm — so the back cover seats correctly without pressure on the battery contacts.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS held cutoff cleanly at the low-voltage threshold and accepted a full charge without tripping the protection circuit under standard 5V USB input.
• Fuel gauge recalibration after swap: On first use after installing this cell, run one full discharge down to automatic shutdown, then charge uninterrupted to 100% before use. The K520's fuel gauge IC was calibrated to the old cell's discharge curve — skipping this step causes the percentage counter to read incorrectly for several cycles.

Why the K520 reports the wrong battery percentage after a cell swap

The K520 uses a coulomb-counting fuel gauge IC that builds its capacity model over charge and discharge cycles. When you swap the cell, that model still reflects the old battery's degraded curve. The gauge will show 100% before the cell is actually full, or drop suddenly near 20–30% as the new cell's actual voltage floor differs from what the IC expects. One complete discharge-to-shutdown followed by an uninterrupted charge to 100% forces the IC to rewrite its reference curve against the new cell.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff, not a calibration error. Under modem or display load, the cell's output voltage drops faster than the fuel gauge percentage suggests. If the K520 cuts off at 20–30% and restarts immediately, the cell is hitting the BMS low-voltage cutoff — approximately 3.0V — while the gauge still reads higher. Run a full recalibration cycle first. If shutdowns continue after two full cycles, check that the battery connector is fully seated and making clean contact on all three pins.