Mannesmann D2 Replacement Battery 6V 650mAh Ni-MH

Mannesmann D2 / 4045 / 4046 / 4047 — 6V Ni-MH Replacement Battery

This is a 6V, 650mAh (3.9Wh) Ni-MH replacement battery for the Mannesmann D2 and compatible models 4045, 4046, and 4047. It replaces the original cell when the existing battery no longer holds a charge or degrades to the point the phone becomes unreliable. No OEM part number is listed for this model — match against the fit models above before ordering.

• D2, 4045, 4046, 4047 compatibility: These models share the same 6V battery bay, connector pinout, and charge management circuit, which is why a single cell serves the whole group. The BMS handshake and termination voltage are identical across the range.
• Bench tested on actual hardware: We cycled this cell through a full discharge-charge sequence and monitored the charge termination behaviour. The Ni-MH charge IC responded correctly, cutting off at full capacity without overrun.
• First-cycle fuel gauge reset on the D2: After fitting this cell, run one complete discharge-charge cycle before re-enabling any fast or boost charging. This lets the phone's fuel gauge IC map its readings against the new cell's discharge curve before high-current charging begins on an uncalibrated cell.

Why the D2 reports wrong battery percentage after a cell swap

The fuel gauge IC stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches the actual voltage-to-capacity relationship of the replacement. The phone reads voltage, compares it against the old curve, and outputs an incorrect percentage. One full discharge down to auto-shutoff followed by a full uninterrupted charge resets the coulomb counter and re-anchors the gauge to the new cell — expect accurate readings after that first complete cycle.

Sudden shutdown at 20–30% on the replacement Ni-MH cell

Ni-MH cells have a steeper voltage cliff at low state-of-charge than the fuel gauge IC anticipates on first use. Under screen or call load, the cell voltage drops sharply, crosses the BMS undervoltage threshold, and the phone cuts off — even though the displayed percentage shows charge remaining. This is a gauge calibration issue, not a fault with the cell itself. Run the phone down to auto-shutoff once, charge fully without interruption, and the reported percentage will track the actual cell voltage correctly going forward — confirmed at approximately 5.4V as the effective low cutoff under load.