https://wiki.openstreetmap.org/wiki/Key:maxstay
I understand maxstay is how long we're allowed to stay before getting a fine. On charging stations, they implementing this by charging your credit card. Once I paid 70€ because I did not disconnect in the 30 mins allowed.

Tagging the price is useful, even if the price changes, so that we don't go to a station which was already expensive before that change. I wish the providers would take care of updating OSM, instead of waiting for the community...

The charging stations I have updated in this changeset were first put by me, on a previous trip through Croatia 6 years ago, and nobody updated in between!