It's a neat idea but I think you're really underestimating how large the battery would need to be to provide any useful range. I have a Toyota RAV4 hybrid whose battery only provides < 1 mile range and its battery is basically suitcase sized. I'm not having any luck finding dimensions or weight but you can get some sense of the size from the pics in this eBay listing: https://www.ebay.com/itm/266168009857