If the minimum batteries are installed in electric cars and you just rented an additional extension pack for long trips this would make the cars cheaper up front exellerating sales.
this does a few things:
1) increases sales of e vehicles toward criticcal mass.
2)Lowers price tag (badly needed)
3)rent extenders as needed. (Could give 2 free weeks a year of battery rental as part of car purchase.
3)Allows for improvements in batteries to be rolled out and used instead of purchasing a new car with new technology.