There is no battery problem for truck-to-door. The truck charges between deliveries and spare swap-in packs pick up any slack if the duty cycle is too high.

It doesn't take a lot of battery power to fly a mile.

Depends on the weight of your package.

in this use case- truck to door, alternatives like compressed air might work ..especially if they can recharge in the truck

I'm trying to think what you'd use compressed air for here, and the only thing I'm coming up with is some sort of parcel cannon, which while awesome does seem to have a few issues.

What am I missing?

To power drones, presumably. You have the example of Tata's compressed-air car prototype http://www.business-standard.com/article/companies/cars-runn...

Although I suspect a compressed air tank with enough capacity would be way too heavy for a drone to carry.

yes - that's the type of thing I'm talking about. I've heard of taxi's running on compressed air motors in dense urban environments ..maybe NYC?.

The power to weight ratio is the key issue. Also -- noise could be an issue too -- want to have quiet deliveries.

although the parcel cannon is a fantastic idea! ..not to different from how my paper is thrown at my house at 4am today :)

I'm thinking parcel cannon + small airbag bumpers and maybe a little parachute to slow decent at exactly the right time :)

compressed air motor (edit>) and tank instead of electric motor and batteries.