Turning the key to the "accessory" position doesn't actually draw any electricity from the battery. It simply allows you to draw a limited amount of electricity to run certain accessories, like the radio, the power windows and the interior lights. ... And that would certainly be enough to kill the battery in 48 hours.

Is it bad to leave car in accessory mode?

In accessory mode you can leave on for hours with no effect, not sure of the total time but in 50 yrs of owning vehicles I've never had a problem with it being in that mode-just relax and enjoy it and don't leave the engine running total waste of your fuel and not good for the environment.

How long will a car battery last on accessory?

A new and fully car battery can stay for around two weeks without needing to be recharged from a generator. This battery will fully get discharged after approximately two to three months. If you leave the battery for roughly two and a half months, you will not be able to start the car engine.