I notice there are what looks like little batteries that are located under the Username of the person who posts a new thread or replies to someone else's. Also, certain ones look like there all charged up and there's four of them. While others are empty and there might be only one of them. What's that all about?

The batteries are charged up by posting.

In general: More batteries=longer iPad runtime

You start with 1 empty battery, once it gets filled, you receive another one to fill up and so on.

The forum batteries under your user name get added as you post. Users with lots of posts have many more batteries. They are also named. iPad noob, Fan, Master, etc, depending on the number of posts you've made to the forum.