About this replacement
Soehnle Scale 7858 — 4.8V Ni-MH Replacement Battery (SOE7858)
This 4.8V 1800mAh Ni-MH pack replaces the internal rechargeable battery in the Soehnle Scale 7858 digital bathroom scale. It restores power to the weight measurement circuit and display when the original cell has lost capacity and will no longer hold a charge. Voltage and connector match the OEM spec.
- Scale 7858 fit: The 7858 uses a dedicated rechargeable Ni-MH pack rather than disposable cells. The voltage rail, connector orientation, and physical footprint of this replacement match the OEM cell — the BMS in the scale expects a 4.8V source, and deviating from that will cause erratic weight readings or a blank display.
- Bench tested on actual hardware: We cycled this pack through charge and discharge on the scale platform, confirming the BMS accepted the new cell without flagging a fault state and that the display initialised cleanly through the startup sequence.
- First-use calibration on the Scale 7858: After fitting the new pack, step on and off the scale twice before recording any measurements. The 7858 maps the battery state during those initial power cycles, and skipping this step can trigger premature low-battery indicators during the first few weighing sessions.
Why the Scale 7858 shows a low-battery warning immediately after a full charge
Ni-MH cells have a relatively flat discharge curve, and the Scale 7858 uses a voltage-threshold method to estimate charge state rather than tracking cumulative current. A new or freshly fitted cell may sit at a resting voltage that the scale interprets as partially depleted until the cell has been through at least one full charge-discharge cycle. The indicator recalibrates to the new cell's voltage profile after that first cycle. Charge the pack fully, run a weigh cycle to draw the voltage down slightly, then recharge — the display should read accurately from that point.
Scale 7858 powers on but resets mid-weigh with no apparent cause
When the strain gauge and display circuit both activate at the moment of load, the Scale 7858 draws a brief current spike that an aged or deeply discharged cell cannot sustain. The voltage dips below the BMS cutoff threshold and the unit resets before a stable reading is captured. This is not a firmware fault — it is a cell delivering insufficient current under combined sensor load. Fitting a new pack and charging it fully to 4.8V before use resolves this.