Ever since the idea of electrical power for cars became a serious proposition rather than speculation one thing keeps occurring to me and I think it may be relevant to the discussion here. Interchangeable modular batteries. The practicality of recharging associated with cars has always looked like a show-stopper to me. It's difficult enough to find anywhere to park, let alone with a recharging socket conveniently available. However the infrastructure for refuelling with petrol is ubiquitous. It's obviously a gross simplification but modular rechargable batteries which can be rapidly swapped would eliminate the problem to some extent. Of course getting agreement amongst manufacturers - whether of car or aircraft - for a common modular battery format is likely to be all but impossible.