Visited yesterday without charging.
I found 10 chargers in the Rietbach Center underground parking. 1 is in front of a reserved parking spaces, the 9 others are in front of unmarked parking spaces. 8 of the chargers have eCarUp QR codes, the 2 others don't have any markings. The reserved charger is one without QR code. Only 7 chargers (1-6 and 8) are visible on the eCarUp website and app, but number 7 does exist and the QR code works. No idea if the last 2 chargers are networked through eCarUp and kept hidden, or if they work completely differently.
I'm not sure who is expected to use this parking. Burger King customers can park in the outdoor parking behind the building. There are lots of free parking spots in the Parkallee next door if you're doing a quick visit in the shops. There seems to be a hotel here, so it's probably the most likely use case for the parking, along with the chargers.
The price sheet doesn't list any opening hours. There are hours indicated above the ramp, which I guess are for the parking: "Mo-Sa 06.00-22.00" During the shopping center opening hours it's easy to re-enter the parking, but I didn't see a night entrance. It's also possible to walk down the ramp from the Burger King parking but I suspect they have a weather door they can close at night and it won't be possible to walk through there.
On the large totem containing the business names, the covered parking sign is combined with a "GOFAST" sign, but there is no GOFAST station here. There are gabarits for a construction in the Burger King parking, so that's where I suppose a GOFAST station is being constructed. I didn't see anything in the underground parking suggesting a fast charger would be constructed, and it would be an odd place to install the fast charger. At the same time, there's very little space outside so it's likely going to be a Langenthal situation.
At the fork off the main road, there are many parking signs as the Parkallee entrance is right next to this one. You need to follow "BurgerKing Drive" / "Rietbach Center - Parking mit Einstellhalle". Once behind the building in the Burger King lot, there is the ramp down to the ticket gate for the underground parking.