I've noticed a really strange pattern with my car and I'm hoping someone can explain what's going on. I have a 2017 Toyota Yaris that I've owned for about three years. During the cooler months from November to March, my battery is completely fine. The car starts every morning with no issues at all. But once the summer heat really kicks in, especially when temperatures go above 45 degrees, my battery starts dying overnight. I'll park the car in the evening when it's running fine, and the next morning I'll turn the key and get nothing but clicking or very slow cranking. This has happened three summers in a row now. I've replaced the battery twice, and the same thing keeps happening. It's like the heat is killing my battery overnight. I've been reading about common causes of battery drain in hot weather and I know that heat can increase internal discharge rates and cause fluid evaporation, but why would it happen overnight specifically? Wouldn't the battery be even hotter during the day when I'm driving? I park in an open lot with no shade, so my car sits in the sun all day while I'm at work. Shouldn't the battery be dying in the afternoon instead of overnight? Could it be that something in my car, like a cooling fan or some other component, is turning on at night when the temperature drops and draining my battery? I don't have any aftermarket electronics installed, everything is stock. Is there any way to test if something is turning on when the car is off? I don't have a multimeter but I could probably buy one if it would help. I'm just so tired of waking up to a dead battery every few weeks during the summer. Any advice from people who have dealt with heat-related battery drain would be really helpful. Please share what you learned and how you fixed it.