We plan on attending
MVMCP in December. My wife will need an
ECV. I am assuming our odds of getting one go up if we arrive early and people turn them in as they leave from their daytime visits. Am I right? I also assume the batteries will probably be run down. Does Disney have to recharge them overnight or do they just swap out new batteries so they can rent them right out again. I know I can guarantee an ECV by using an outside vendor but gather they don't deliver to the parks. We are staying off site and can't see us being able to rent one and get it to the park.
Let's break down your concerns one by one:
As you probably know, you can arrive as early at 4:00 pm for the Party. This is a fine time to get there, simply because a certain percentage of folks will start moving around all over WDW towards their dinnertime plans. But just so you know, since the Parks
ECV rental can be "hopped" from one park to another during the course of the day, the inventory of available
ECVs at any of the 4 parks can - and does - fluctuate.
The units that Disney rents out are *heavy duty*. Think of those heavy-duty shopping cart beasties at the grocery store or Wal-Mart, but without the big wire basket on the front. In theory, the batteries in those units should be able to run on a single charge from open to close if needed. Yes, there are exceptions to the rule, but WDW CMs are pretty consistently solid on not renting out an ECV that is going to croak.
Finally, some vendors *will* actually deliver to the Parks, (and meet you outside bag check, for example) however most vendors will require at least a 24 hour rental, and many require 2 or 3 days at a minimum... so yes, you would have to be able to take it with you when you leave after the party. There are rental ECVs that can be disassembled into (relatively) easy to manage pieces, but you will need to be able to fit those into whatever vehicle you are using to get back to your lodging.
Hope this helps answer some of your questions!