Things like seat heaters and your car stereo tax the vehicle’s electrical system. Starting the car draws on the same system heavily; if your battery is being tasked with running accessories and your starter motor at the same time, it’s going to have to work a little harder. As an illustrative example: if you start your car with the headlights on, you may notice them dimming as you crank the starter. Some vehicles have an extra battery for accessories and will be less affected by an extra draw from starting. However, even the owner’s manual in a modern Acura suggests turning off accessories at idle speed and below to guarantee maximum battery life and minimum strain on related components.