Recently I was using a small dust buster-type vacuum cleaner for my SUV which I plugged in to the cigarette lighter in order to use it. I only turned the car on (so that the radio could be turned on, etc.) but not the ignition/engine. I was told that doing so would put pressure on the battery and drain it.
Is this true? When using my vacuum cleaner or portable tire inflater, should I only turn the car on, or should I turn the key all the way to actually start the engine?