Visited today without charging.
I thought the parking was closed on Sunday but there were a number of cars there. I didn't try entering by car myself. Looking at the parking tariff sheet (unchanged from last time) it might actually be the underground parking only that closes evenings/Sunday. So the charging stations might actually be accessible 24/7.
I have finally been able to see the Kempower all-in-one in person. Unfortunately it seems to be out of order. It seems to alternate between all out of order and all occupied in the live data.