I was at The University of Warwick for a conference. In theory they had car charging places. These weren’t specific car charging ports, just standard three pin plus sockets.
I was down to under 15%, plugged my car in and headed off to the conference.
When I went to get my car, after eight hours on charge it now had a 69% charge.
It took about another eight hours on another day to get to 100%.
Informative experience.