Qtek PC20B 7070 Replacement Battery 3.7V 1150mAh

Qtek 7070 — 3.7V Li-ion Replacement Battery (PC20B / PC26A)

This is a 3.7V, 1150mAh Li-ion cell for the Qtek 7070 Windows Mobile PDA phone. It replaces OEM parts PC20B and PC26A. The cell fits the original battery bay and connects to the device's charge IC and fuel gauge circuit directly.

• Qtek 7070 fitment: The 7070 uses a single-cell Li-ion pack with a three-contact interface — positive, negative, and a thermistor line the charge IC uses to monitor cell temperature during charge. Both PC20B and PC26A share this connector layout, which is why both part numbers apply to the same slot.
• Bench tested on actual hardware: We ran the cell through charge, full discharge, and a second charge cycle on a 7070 unit. The BMS accepted the handshake on the first connection, charge IC entered CC/CV mode normally, and the fuel gauge registered state of charge without a manual reset.
• Fuel gauge recalibration on first use: After fitting this cell, disable any sync or data-heavy tasks and let the phone run through one full discharge down to auto-shutdown, then charge uninterrupted to 100%. The 7070's fuel gauge IC calibrates its coulomb counter against that first full cycle — skipping it causes percentage jumps for the first several days of use.

Why the Qtek 7070 reports wrong battery percentage after a cell swap

The 7070 uses a fuel gauge IC that stores a charge curve calibrated to the original cell's internal resistance and capacity. A new cell has a different impedance profile, so the stored curve no longer maps accurately to actual voltage readings. The result is percentage values that lag or jump — the gauge is reading voltage correctly but interpreting it against the wrong model. One full discharge-to-shutdown followed by a full uninterrupted charge resets the coulomb counter and re-anchors the curve to the new cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops sharply under load — typically during GSM radio bursts or screen-on activity — faster than the fuel gauge predicted. The old calibration curve expects the original cell to hold voltage at that state of charge; the new cell hits the BMS low-voltage cutoff at 3.0V before the OS has time to trigger a graceful shutdown. The fix is the same recalibration cycle: one full discharge to auto-shutdown, then a full charge. After that cycle, the fuel gauge tracks the new cell's actual voltage cliff and the OS gets enough warning to shut down cleanly.