Three modes:

Air Stations between one and three minutes depending on the vehicle:

The air is compressed in tanks at the air stations using a multi-stage compressor. 
The stored compressed air is transferred from the air stations’ tanks to the vehicle’s tank).
The air compression in the station’s tanks can be performed by using renewable energies (rivers driving micro turbine connected to the compressors, wind etc…).  

Electric plug between 1h 30 mins and 4h 30 mins depending on the vehicle:
        
When the vehicle is equipped with an onboard refilling system, the refilling of its tanks can be carried out by connecting them to a domestic electric plug.
The moto- alternator, (used when the vehicle is running to retrieve energy during braking and decelerations phases) drives the air engine operating in ‘compressor mode’ to recharge the tanks. 

While running in the dual-energy mode:

When the vehicle is being driven by a dual-energy engine, the refilling of the tanks can be performed by sharing the energy.
While running (an energetic adjuvant’s combustion, see dual-energy above), the compressed air tanks are refilled using a booster.
The time needed to fill the tanks will in this case depend on the speed at which the vehicle is being driven, thus of the ‘surplus’ of the needed power that refills the tanks.

Depending on the refilling mode, 100 km downtown cost between € 0. 50 and 1.5 €.