Apple will replace your iPad only if the battery has lost its charge through normal use. So if you make your battery kaput by spilling hot coffee on your iPad or accidentally dropping the device out the window, you're out of luck.
And beware that the replacement iPad won't have any of your personal data on it. You'll need to make sure you have a fresh backup of your contacts, calendars, e-mail account, and other information.
(Lance Whitney. When your iPad battery dies, dig out $99-plus. CNET News. March 16, 2010.)