OP here...

As others have said, I was mostly referring not to the ability to easily convert to and from aluminium, but instead the fact aluminium is easily transportable and such a useful material that there is rarely surplus (if aluminium were cheaper, it would take over lots of places where steel is used, and even some uses of concrete).

That in effect means that if there is excess electricity in a region, it can in many cases work out cheaper to build a decent road to the region and build aluminium smelters than to build power transmission lines out of the region.

I think the OP just used this figure of speech to illustrate the amount of energy that goes IN, not to say that you can get it easily out again.

But then there is this: https://en.wikipedia.org/wiki/Aluminium%E2%80%93air_battery so who knows.