New Battery technology
There is a new Lithium battery that is due out in under 5 years.
Lithium Air, this battery could have an energy density of up to
5kwhours/kilogram. IBM are working on it and Japan with some success.
As Avgas is 12Kwh/kg but engines are only 25% efficient then it means only 3kgwh/kg is used, as electric motors are 85% then any battery about 4kwh/kg or over is about the same as Avgas.
These batteries can be recharged or the lithium & electrolite with a cassette can be replaced to recharge them, 10 minute to refuel. So a rechargable or lithium fuel cell.
Please forget about hydrogen it will never happen, just to difficult to implement and lower over all efficiency never mind the cost.
So by 2020 nearly all cars will be direct electric drive and light weight in wheel electric motors/brakes, no mechanical brakes, will be normal, 120Kw at 66lbs. These are available to day, Volvo and Ford are building demo cars and trucks with them.
So electric aircraft will be feasible, with good range and carry capability.