Where are they located? Did you stay in your i3 or is it a short distance to the shopping centre?I tried these and they are currently free of charge. Probably a promotion by Engenie.
The parking advisor had no clue about the free parking and he called his supervisor who wasn’t aware either. To avoid a penalty I paid £5 which allows you to stay up to 4 hours. I charged my i3 80% in just over an hour.