Philips P820 Compatible Battery 3.7V 700mAh A20KAL/GZP

Philips P820 Series — 3.7V Li-ion Replacement Battery (A20KAL/GZP)

This is a 3.7V, 700mAh Li-ion cell for the Philips P820, P826, 822, and 825 smartphones. It replaces the original A20KAL/GZP battery when the existing cell can no longer hold a charge or causes unexpected shutdowns. Voltage and capacity match the original specification exactly.

• P820 / P826 / 822 / 825 compatibility: These four models share the same battery bay dimensions, connector pinout, and 3.7V nominal rail. The BMS handshake on each device expects the same charge termination voltage, so one cell revision covers all four.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the P820 platform. The BMS accepted the cell on first insertion, hit full charge termination at 4.2V, and stepped down correctly through low-voltage cutoff without triggering a protection fault.
• Fuel gauge recalibration on first cycle: On first use after installation, run one complete discharge-charge cycle with fast charging disabled. The fuel gauge IC in the P820 calibrates its coulomb counter against the cell's actual discharge curve — skipping this step leaves the gauge reading against the old cell profile and produces inaccurate percentage readings from day one.

Why the P820 reports wrong battery percentage after a cell swap

The P820 uses a fuel gauge IC that tracks charge state by measuring cumulative current flow — a coulomb counter. When the original cell degrades, the OS recalibrates around the reduced actual capacity. A new cell with full 700mAh capacity has a different discharge curve, so the old calibration data produces readings that drift or jump. One full discharge to auto-shutoff followed by a complete uninterrupted charge resets the coulomb counter against the new cell. After that cycle, percentage readings stabilise.

Sudden shutdown at 20–25% on the replacement cell

This happens when the modem or display pulls a brief high-current spike and the cell voltage dips below the BMS cutoff threshold — even though the reported percentage still shows charge remaining. On a new cell that hasn't been calibrated yet, the fuel gauge maps this voltage cliff inaccurately, making the shutdown appear to come early. Run one full calibration cycle first. If shutdowns continue past that point, check that the battery contacts in the bay are clean and making solid contact — a resistive connection amplifies voltage sag under load and triggers cutoff at a higher state of charge.