iPods sure look svelte and stylish without a battery door, but the omitted hatch makes the whole thing worthless if your battery gives up the ghost. All batteries degrade through time and use; expect your iPod's to last between one and three years.
Today's batteries work best when kept plugged in as much as possible, rather than being allowed to run down, and your iPod will last longer if you keep it charged as often as you can.
Once the iPod's battery can't keep a charge, you can pay Apple or a repair shop to replace it. But you can do it yourself for about half as much money, and in many instances you'll get a better-performing battery than the company originally provided.
Most iPods open in a similar way: The front upper half with the screen lifts away from the metal backing. Many sources of replacement batteries provide instructions for specific iPod models. I purchased a new battery for my iPod Video (fifth generation) through Juice Your iPod (ipodjuice.com) for less than $30.
First, turn off the iPod and lock the Hold switch. You'll need to wedge something between the two halves to release the internal latches. A tiny flathead screwdriver would be likely to gouge the plastic front or the metal backing. Some battery kits include plastic tools that are safer; guitar picks can also do the job.
Carefully, but with the necessary force, work a plastic wedge into the seam along the side. Aim the tip toward the device's back; the metal backing cradles the front, so that's the only direction for the tool to travel. Once your tool is inside, gently work it around the iPod's edges. The case might try to snap shut where you just opened it, so I like to leave extra guitar picks in place.
Separate the metal backing from the front carefully-a thin ribbon cable connects them. Use a small screwdriver to lift the plastic latch holding the battery cable to the iPod. Once you've freed the battery, remove and replace it. Seal everything back up; the pieces will snap back into place. Last step: Recharge the iPod.