Idling charges cars*;
Shut off music, don’t hit brake
When you turn on car.**
*and not driving on the freeway, like I thought! I guess battery design changed in the early/mid 2000s.
**if your car battery is 12V and it takes 9V just to start your engine, then on cold mornings the idea is to shut off any accessory you can, as each accessory has an associated voltage requirement. So your radio, the heat, those windshield wipers you forgot to set to neutral, even holding down your brake (as I was taught to do in driver’s ed) causes the brake lights to come on in the back