Unable to answer "How many cars can be charged here at the same time?" for https://osm.org/node/6537368831 via StreetComplete 53.0:

The only thing I can find is a power outlet for boats. One could probably load a car here (as with any power outlet) but I doubt that is the intention of this map object.

Attached photo(s):
https://westnordost.de/p/152191.jpg