It's actually really simple and if you have the right stuff around, costs free dollars, unlike $70 plus iPod docks.
Also, you get louder sound and basically a free iPod dock without the charger. Although, it does save a lot of battery. I have a 2GB Gen1 Nano, which, when it has that last sliver of battery, usually lasts about 2 minutes. This little idea stretched out that last sliver to an hour. Basically, it gave me a 3000 percent boost, and cost nothing. I have no idea how it works with other iPods or if my results were even correct but I'm sure it will at least get you a noticeable battery life extension.
It works off the concept of the iPod having to supply electricity to the earphones you use. When you use a method of sound transport that is separately powered, the iPod doesn't have to supply it power.
Step 1: Obtain Your Speakers.
Get some USB or AC powered speakers. I had these ones lying around and they have decent quality.
Step 2: IPod, of Course.
Seriously, if you need an explanation for this one, go see a doctor.
Step 3: Connections Are for the Win.
Sock everything up. Connect your speakers to the ipod and connect your speakers, if they're AC, simply through the socket. If you have USB speakers, you can either find an adapter for USB to AC or connect it to your computer, although this defeats the purpose of the Instructable- if you have a computer anyways listen to music through the computer.
And for those who say, "Just use your ipod wall charger." that also defeats the purpose of this instructable. This is for when, say, you don't have your iPod to USB connector or something.
Step 4: Turn It Up and Enjoy.
Fire up your iPod and speakers. You can turn up the iPod as much as you want without worrying about battery, since again, the iPod is only sending a signal and not power.
Sure, it's a simple and fast solution but I found it really helpful for my own purposes.