From what I know about leet. It started as a sort of shorthand in electronic communication. Not a kids invention. Later kids picked it up and modified it to make it cool.

MP3 players eat batteries indeed. My first one was a very cheap stick. I expected it would run for some 40 hours at least on 1 AAA size, maybe even more Oh shock and horror, it quit after 4 hours!

I've looked around a bit, and saw that this was normal for such players. 20 and even 10 hours is regarded splendid. There's one that promissed 70 hours, it can contain several albums and costs a bit more. That 70 hours depend on how you use it and also what format you use, I get some 50+ hours. It's a nifty little device, ships with good software, easy to operate; why didn't I have it 15 years ago instead of that bulky Walkman?