German argues that lighter and more powerful electric motors, batteries that can store more energy, and more sophisticated aviation software could transform the market for small aircraft.

Each time batteries improve, electric airplanes can be a little lighter and fly a little farther on a single charge.

German says battery technology isn't quite there yet. He predicts the energy density of batteries will need to approximately double for small electric airplanes to really take off.

Highlights

* analyst indicates energy density of batteries needs to roughly double for small electric planes - flying cars to boom
* solid state batteries could could double energy density of batteries. Progress is being made to commercialize metal solid state batteries with the required energy density

Batteries don't improve as rapidly as computer chips, so it's hard to say exactly how quickly batteries will improve. Tesla CEO Elon Musk, who is currently building a giant battery factory, has said that battery density typically improves by 5 to 8 percent per year, which implies that density could double in the next decade — though that could require finding new battery chemistries.