Car Batteries are Sensitive to Heat and Cold
It is difficult to come to terms with sometimes, but the reality of life is that car batteries are sensitive to changes in temperature just like human beings are. In fact, we don't often realize that car batteries can be impacted by the cold just like they are by the heat.
Heat tends to warm up chemicals in the batteries that can cause those batteries to erode and take on damage in that way. There is a lot of acid in car batteries, and that means that the potential for that acid to spill over onto the battery in the heat is very high and potentially damaging. Thus, all vehicles should be kept out of extreme heat whenever possible.
Cold has a negative impact on batteries as well. When you are dealing with the cold you are concerned that the battery may literally freeze and thus become unusable as well. Either side of this spectrum is something that you want to avoid if at all possible.