I’m a little late seeing this, but if you haven’t started your trip yet, you might still need info.
If you rent from the park, and turn it in either to take a break or to go to another park, you can just present your receipt and not have to pay again. BUT they will not hold the
ECV for you. If you turn it in, if there is a waiting list of others waiting for an ECV (and there almost always is), then it will be rented to someone who’s been waiting for one.
When you return, there may or may not be one available. The same applies to going on to another park. You may end up on a waiting list when you first arrive, and you’ll be called when someone returns one.
Some people coming back to the same park, have stashed their ECV in an out-of-the-way spot while they’re gone, and retrieved it when they return. (Never leave belongings that you care about losing). There is a risk that a CM who notices an ECV parked like that may decide it’s abandoned and return it to the front. If that occurs, the procedure is the same as for a “lost” ECV… you go to the rental counter and if there’s one available they’ll give it to you, but you may be put on a list. (At DLR, they’ll give you a standard wheelchair to use while you wait… but that assumes you have a pusher which of course isn’t always the case. Idk if they do the same at WDW)
This is why people here often suggested that guests consider an off-site rental. (There’s a pinned list of common vendors at the top of the board) The benefit is you have it at the resort, to and from transportation, and in the parks and wherever else you might go. The off-site equipment fits on busses and boats and the skyliner.
If you’re going elsewhere around Orlando/Kissimmee, there are accessible Mears Taxis (and Lyft vehicles although they often send the request to Mears). Our experience with Mears was overall very good. We had a couple glitches, but we were generally happy overall.
Or if you have a rental car, there are off-site options that can disassemble and fit a trunk.
Hope you have a good trip!