Humantechnik Sydney Replacement Battery 3.7V 900mAh

Humantechnik Sydney — 3.7V Li-ion Replacement Battery

This is a 3.7V, 900mAh Li-ion cell for the Humantechnik Sydney mobile phone. It replaces the original battery when the cell can no longer hold a usable charge. Dimensions are 53.00 x 34.00 x 4.80mm — confirm these against your existing cell before installing.

• Humantechnik Sydney fit: The Sydney is a dedicated mobile phone with a fixed battery bay sized to this cell's footprint. The voltage rail and connector orientation match the original spec, so the charge IC communicates with the new cell without hardware modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS accepted full charge without tripping protection cutoff, and voltage held stable across the discharge curve with no anomalous mid-cycle drops.
• Fuel gauge recalibration on first cycle: On first use after installation, disable any fast-charge mode and run one complete discharge-charge cycle. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging begins on an uncalibrated reference.

Why the Sydney reports wrong battery percentage after a cell swap

The fuel gauge IC on the Sydney stores a discharge curve profile calibrated to the original cell. When a new cell goes in, the IC still references that old curve, so the percentage shown on screen does not match the actual cell state of charge. This gap causes the phone to report 40% while the real cell voltage is already near 3.5V. One full discharge to auto-shutdown followed by a full uninterrupted charge resets the coulomb counter and re-anchors the gauge to the new cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC has not yet recalibrated and the cell hits a voltage cliff under screen or modem load. The Sydney's processor draws a current spike that pulls cell voltage below the BMS cutoff threshold — around 3.0V — even though the gauge still shows charge remaining. The phone cuts out to protect the cell. Run two full discharge-charge cycles without interruption, then check that shutdown no longer occurs until the gauge reads below 10%.