The slides on the Winnebago c-class work off the chassis battery. Shore power does NOT charge the chassis batteries unless a trik-l-charge or other battery maintainer has been added after leaving the factory.
Get out your multimeter and check the coach battery voltages. Also check the connection terminals. On our 29b, the batteries are located under the entry step, just ahead off the rear wheels and would always get dirty and good connections until cleaned. Finally covered the tops with heavy plastic garbage bag.
Beverley&Ken