First it sounded like a joke. A lens mounted upside down on a FE2... How is that possible with the Nikon mount? It must have been forced in there.
Bring it to your local repair shop, seems to me the best thing to do.
As for the batteries, yes indeed the usual 1,5V LR44 type fit all Nikon cameras made between 1959 and 1988, F4 being the first to use AA type.