Requires a constant 230V. Battery only for maintaining the negative pressure in the event of a power failure.

the winbot is operated with a mains cable. the battery is only for emergencies if the power supply should fail for a short time so that the winbot does not crash.

Hello Urs
Yes, the appliance only runs on battery power for a short time if the appliance fails. I suspect that most or even all devices are still connected by cable because the battery is too heavy and the suction power at the window would be too low and the risk of falling too high.
We have stuck the fall protection cable to the front of the Winbot, as otherwise it would get tangled up with the power cable and the enormous suction power means it doesn't need a fall protection cable. The suction power is very good and we are very satisfied with the overall package.
For price reasons, you can also buy a normal window cleaner and not necessarily the expensive proprietary window cleaner. But be careful: please test which product meets your requirements first. There are also videos and tests available.
We use the Ecovacs window cleaner and this is also designed for the device, but is a little expensive.
In general, we can only recommend the device.