Visited yesterday without charging.
The chargers are in the paid parking of the "Elektro-Ausbildungszentrum".
There are ticket gates and a payment machine but they didn't seem to be working at the moment. Of course it's the holiday so they might just have disabled it for now.
The payment machine has a sign saying "Neuer Kassenautomat" and that new payment methods are available. Not sure how new this is though. The sticker on the machine say 15min free, 60ct/h, Mon-Sat 06h-18h. Not sure if you can park for free the remainder of the time or not enter at all.
The payment machine is just out of frame in my pictures, it's to the right, against the next building.