Re: @45RPM
Nothing that flies or has to travel long ranges can get by without fossil fuels at the moment, the most practical replacement is fuel cell technology that's only starting to mature and even that isn't as good. ex: By a conventional approximation of power required to lift a given mass of helicopter, one where every single component was also 100% battery in addition to its function would be able to hover something like 1-1.5 hours? That's using cutting edge batteries.
In some application it's very, very important how much power density you can get.