Which means you can freely leave that USB charger plugged into the car’s 12V jack if you want, provided you don’t plan on putting the car in storage for around 117 days, that is.

It’s all about the amperage. This situation is all to do with amperage. USB ports at home, such as those of a wall plug or on the side of your laptop, tend to have an output of 2.1A or 2.4A.