BenQ P51 Replacement Battery 3.7V 1400mAh 2C.2G3.D0.101

BenQ P51 — 3.7V Li-Polymer Replacement Battery (2C.2G3.D0.101)

This is a 3.7V 1400mAh Li-Polymer replacement battery for the BenQ P51 mobile phone. It matches the original OEM part number 2C.2G3.D0.101 and fits the P51's battery bay directly. Capacity is 5.18Wh — identical to the factory cell.

• BenQ P51 fit: The P51 uses a single Li-Polymer cell on a 3.7V nominal rail with a three-contact connector — positive, negative, and a thermistor line feeding the charge IC. This replacement matches that pinout and cell geometry exactly. No connector modification needed.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on a smartphone charge IC testbed. The BMS accepted charge handshake without error, thermistor line reported within expected resistance range, and the cell held voltage above 3.6V through the bulk of the discharge curve.
• Fuel gauge recalibration on first use: On first installation, run one complete discharge down to auto-shutoff, then charge uninterrupted to 100%. This gives the P51's fuel gauge IC a reference curve for the new cell. Skip this step and percentage readings will drift — often reading 30% when the cell is nearly flat.

Why the P51 reports wrong battery percentage after a cell swap

The P51's fuel gauge IC stores a learned discharge curve from the previous cell. When a new cell goes in, that stored curve no longer matches the actual voltage-to-capacity relationship of the replacement. The IC reads a voltage and maps it to the wrong percentage based on the old data. One full discharge-charge cycle resets the coulomb counter reference and brings percentage display back in line with real capacity.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops sharply under load — a voltage cliff — before the fuel gauge reaches 0%. The modem radio and display together can pull enough current to cause a sudden voltage sag below the protection threshold, even when the reported percentage looks safe. The P51's charge IC will cut power the moment cell voltage drops below roughly 3.2V under that load spike. Running the full recalibration cycle first reduces the gap between reported and actual charge state, which moves that cliff closer to where the OS expects it.