Hybrid aircraft have no technical connection whatsoever with hybrid cars.
Hybrid cars are mostly efficient in city driving because they can get some of the energy back in when braking (particularly for city busses). Plug-in hybrids are also nice where you get some cheap and short go-to-work city-range purely on electricity.
Aircraft can't use regen because when you descend, regen creates drag and increases descent slope which means your top of descent needs to be some further distance away and the energy you need cover that distance is ALWAYS (look up entropy) going to be more than the regen energy of the descent, with the exception of poorly planned mostly speed brakes deployed descents.
Where hybrids start to make sense on aircraft is when you consider the wildly different power requirements of flight segments like taxi, takeoff, climb, cruise and descent, and you discover that on short haul aircraft your turbine engine sucks terribly most of the time except when near full power (piston engines don't suck so bad at low power and are less desirable in hybrids). Then you can scale down the turbine engine and pair it up with electric power assistance, and if you do it right you end up with a significantly reduced block fuel - even considering generator losses. And that's only the beginning of possibilities.