Economy mode

The car has an economy mode designed to preserve the battery and comes into effect after a period of time when the engine is turned off. The manual states it will come into operation at some time within an hour of the engine being turned off. My last C5 used to come in after 1/2 hour, however with this car which I bought in Sept, it comes in after just 4 minutes of turning the engine off. This means that after 4 minutes I cannot listen to the radio, cd player or operate the windows. Each time I get into the car it is in economy mode and therefore the same problem of no windows or radio. If I am parked and want to use any of these electrics, I have to run the engine ! I have discussed this with the dealer who tells me its to protect the battery, but I am using the engine and fuel just to listen to the radio or wind the windows down if someone wants to talk to me from outside of the car. Is this a fault ? and if not, can it be disabled as it is a useless bit of equipment.