It would be great if they standardised battery packs and made them configurable. So you don't need all that weight being carried around when it isn't needed, or you could rent more batteries for long journies if you rarely travel very far, maybe exchange cells instead of charging along the journey. Two-car(+) households can pool their batteries for going on holidays etc.

I don't think it will happen though. It would be tricky to get the right size/ weight that most people can carry without making it tedious (wouldn't be fun swapping 18650s around). Any larger and people would need hoists or jacks, then the is the issue of how to quickly & easily secure these large battery packs...