I have a used RL850 robotic lawn mower for sale. I used it at my old house, but cannot use it at my new place.
It does need a new battery, a search online will show you countless compatible batteries from a large number of sources. No concerns with the mower beyond that, it has worked flawlessly, but the battery was old and froze over winter.
It includes the mower as well as the perimeter control box, and the owner's manual, all with the original packaging, but not the perimeter wiring (it is basic single wire 14 gauge from any big box store).
You can search online for information about the mower (but i also have the manual for you), but the short version is that you run a wire around the perimeter of the yard, and also around garden beds and such, so that it knows where to mow. Turn the perimeter control on, then set it out, hit go, and it will work its way at angles across the yard (the same way a Roomba vaccum does). It has safety bumpers to turn around in case it hits a tree, someones leg, etc, and it also will brake/stop the blades should the front wheel be lifted, so they did have safety in mind when designing it.
You get a lot of curious people stopping and watching it to its job, but you can sit back and have a drink in the summer heat while it does the mowing for you (we all know the kids wont mow without a huge argument).