I hope the previous owner is going to help you switch out the batteries. Removal of those dash panels is a real PITA, especially the first time. You might not believe you're really supposed to bend those plastic parts so much to get them free, for one thing. Plus oddball fasteners, jiggling and wiggling of slots and tabs, lining up three different layers of holes for the screws to put everything back together again . . .
Another thing is the nuts under the two battery posts are not captive, so when you disconnect the terminals, the nuts have a way of falling down into the innards of the motorcycle, never to be found. If you don't lose them, they're also tricky to re-connect. I jam something under the nut from the bottom to hold it tight against the terminal while I'm trying to thread the bolt back in. That helps.
At least that's how my Gen I is, and I don't suppose the Gen II is a heck of a lot better. After a few times it's pretty routine, but that first time, wow. HOWEVER. If you buy the bike, it will all fade away, replaced by the glow of happiness shared by ALL FJR riders. Have fun.