Charging of the battery can take place during deceleration or going down a hill. However, due to the small battery capacity, recapturing the energy from climbing a mountain cannot be done in the same manner as a pure electric, which hardly needs to use the brake at all on descent. Ultimately it still requires gasoline for all of it's power. These cars are being advertised as electric cars that don't need to be plugged in but this is extremely misleading because the inability to plug in the car is actually a disadvantage. Pure electric vehicles take about 3 seconds to plug in when you arrive home at night and 3 seconds to unplug in the morning when you leave, many would consider this a lot more convenient that going to the gas station even if you only had to gas up twice a month.
Electricity is also a lot less expensive than gasoline.
With a special meter from the electric utility, an EV can be charged up for as little as a penny a mile and public chargers at shopping malls and restaurants are free. Even if hybrid vehicles can attain in practice a mileage of 65mpg, which is not at all certain, it would cost bout 2.5 cents per mile. Since a hybrid is almost always burning gasoline, that means the hybrid is almost always polluting. Even if it's polluting at an Ultra-Low emission vehicle rate, it's still creating about 30 times the pollution that a pure electric drawing power generated in California would. Of course if you elect to buy your electricity from a renewable energy provider than you can drive a truely ZERO emission vehicle with a pure electric.