When alkaline in a battery wears down, it produces a gas that fills the inside. To test the batteries, you don't have to use a voltmeter or any other device, instead you can simply drop them vertically from a short distance on a hard surface.

To tell if it's got juice, a charged battery will make a solid thump sound and often remain standing. A dead battery will make a muffled sound, and bounce repeatedly, and topple over.

[YouTube via The Awesomer]