Batteries are essential in our everyday lives. But their prevalence doesn't necessarily mean that it's easy to understand how they work. In this video, the engineering guy Bill Hammack takes a look at perhaps the most basic battery of all—the lead-acid cell—in order to explain the fundamental science behind every single battery you've ever used. Building on that basic knowledge, he also explains why you can't use the same battery for every single application; so now you know why your car doesn't use LiOn. [YouTube]