The battery's never been replaced, but I've kept a regular eye on it and there's no leakage. There's a couple of small scratches on the motherboard around the holes for the slots, but there's no traces through that area so no problem.
Hardware is fully functional, and the case is in decent condition. All the plastic tabs are present, but there's a few scratches in the paintwork (the rest of the case is sheet metal). There's some yellowing, but it's the Commodore brown colour (similar to the front of the 2000) rather than the beige used on the 3K, so it's not so obvious. It's mostly been kept out of direct sunlight.
The only real downsides are that a hole's been drilled in one of the drive bay faceplates (some previous owner had a switch hooked up to switch between NTSC and PAL, but it's the same design as used on pretty much any Commodore system, so easy enough to replace - I may try to do so before selling it), and that there's no 3500 sticker. I've seen some early photos of 3500s lacking those, so it's possible that the machine was early enough to lack them.
It's currently in the UK, so I'd imagine that shipping to the US would be rather expensive. Unsurprisingly, it's also got a 240V PSU. I'm currently looking at trying to replace it with a desktop 3000, so the final configuration is likely to depend on that.
Anyway, when I've decided what to do with it, I'll let people know :-)