BlackView BV5800 Replacement Battery 3.8V 5200mAh Li-Polymer

BlackView BV5800 — 3.8V Li-Polymer Replacement Battery (V685780P)

This is a 3.8V, 5200mAh Li-Polymer cell that replaces the original V685780P battery in the BlackView BV5800 rugged smartphone. It fits the BV5800 directly — same connector, same physical footprint at 80.40 × 56.20 × 6.40mm. Swap it in when the original cell no longer holds a full day of charge.

• BV5800 fit: The BV5800 uses a single-cell Li-Polymer pack at 3.8V nominal. This cell matches that voltage rail and the connector orientation on the BV5800 mainboard. No adapter or modification needed.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the BV5800 platform. The BMS handshake completed normally, charge IC accepted the cell without fault flags, and voltage held stable across load transitions between idle and active screen states.
• Fuel gauge recalibration after swap: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the BV5800's fuel gauge IC recalibrate against the new cell's discharge curve before high-current charging pushes current into an uncalibrated cell.

Why the BV5800 reports wrong battery percentage after a cell swap

The BV5800 uses a coulomb-counter fuel gauge IC that builds its capacity model from the original cell's charge and discharge history. When you install a new cell, the IC is still running the old model — so the percentage it displays is based on the wrong curve. The mismatch is worst in the middle of the charge range, where the old and new discharge curves diverge most. One full discharge-to-shutdown followed by an uninterrupted charge to 100% forces the IC to recalculate its endpoints against the new cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC has not yet mapped the new cell's voltage cliff — the point where cell voltage drops sharply under modem or display load. The phone shuts off because the cell voltage dips below the BMS cutoff threshold even though the reported percentage still reads above zero. The fuel gauge IC is reading a state-of-charge estimate, not live cell voltage, so the two diverge at high-load moments. Run two full discharge cycles to allow the IC to anchor its low-voltage cutoff estimate to the new cell's actual 3.0V floor.