With the recent unveiling of the new BMW i3 electric car came the announcement that BMW would offer its customers an option called "add-on mobility" that would allow them to use a full-size BMW X5 SUV up to several weeks per year, either for family trips, as a backup, or whenever needed.
It's not a bad idea per se, but there are a few things to consider:
Firstly, I've personally never been that worried about EV range anxiety. It is a real issue, but the media has grabbed on to it and blown it all out of proportions. Is it possible to run out of juice in an EV? Yes. Just as some people run out of fuel in gasoline-powered cars, it's a real possibility, but if you use some common sense, it's not that big a problem, and with each passing month that problem gets smaller and smaller as more charging stations are installed everywhere and as lithium-ion batteries get better and cheaper.
Part of the issue is that people overestimate what they need (the vast majority of trips for the vast majority of people are quite short), and compare apples and oranges. Gasoline cars have a huge range when the tank is full, but you don't fill up every day, so you might spend many consecutive days driving around with just enough fuel in the tank to drive ±100 miles... Yet that's no big deal. With an EV, you can almost always charge overnight, so you start each day with a full charge. Total range is much smaller, but it doesn't need to last you a week or two like in a gas car... It's only a problem for long trips, which for most people are rare.
Secondly, while it's cool that BMW would officially offer the option of having access to a second vehicle for longer trips or when you need to carry more stuff/people, it's not really something new. People could always go rent a car or pay for a car-sharing membership for those occasions when their electric car won't do. Maybe it's good that the option is offered officially because it's more reassuring, and maybe it'll attract more media attention to the fact that any limitations of EVs can easily be worked around simply by renting a vehicle that meets your needs when you need it (which makes more sense than buying a big SUV or truck for just the 5-10 days a year when you really need it).
But maybe that's the clever part, maybe I'm under-estimating the psychological impact and added convenience of this approach. If it does reassure people and lead to more electric car sales, then car rental and car-sharing companies should partner up with electric car makers so that there's an easy way to bundle up the price of having access to another vehicle. Either way you'll pay for it - there's no such thing as a free lunch - but human psychology makes a hundred bucks seem smaller when it's bundled with a larger purchase than when it's a standalone expense. Hey, that's irrational, but if it works...