With modern vehicles, you’ll also find that engine cooling fans and other systems will keep running after the ignition is turned off to, for example, quickly cool down the engine and prevent the water in the engine from boiling. CONTINUAL POWER DRAW, WHEN PARKEDĮven while your car is off, your battery provides power to things like the clock, the radio, and the alarm system, although these things shouldn't have a major impact on your battery. And that is without any drains on the battery. That may not sound a lot, but if we consider that a fully charged battery is at 12.72V and a chemically discharged battery, at which point you’d struggle to start the car, is at 11.8V, in just eight months of non-use, the battery could appear flat. Your standard lead acid battery will naturally drain at 0.1V per month – even sitting on a shelf.
