I have an I Pad 1 for approx. 14 months & have used it for an average 1 hour each day. Have always kept the battery topped up. I don't believe that I got Apple's claimed 9 hrs. life from the start but it's now fallen to about 3 hrs. Is this normal life expectancy before I need to buy a new battery ?
Have you recently updated to iOS5? There's been some battery issues related to that (it really drained my iPhone, but 5.01 seems to have fixed it for me). That's the easy fix if it's a recent issue.
Bad news is that you can't replace the battery, once it's gone it's gone and the whole product needs replacing. But also, while there's the warranty, remember that there is still consumer protection for electronic goods that goes beyond the warranty, so if it is a hardware problem you still have rights.
Assuming it isn't a hardware issue, there are other things that can eat up the battery. When you say you're using it for 1 hr a day, what are you using it for, but more importantly are you quitting the apps you use or are they still running in the background? This is realy iOS 101, so I'm sorry if you're familiar with this and it sounds patronising; double tap the home button and you should then get all the apps that are open along the bottom of the screen. Depending on the app, they could be using up battery even though not using RAM. To close them, press and hold one of the icons and a small "x" will appear and the icons will do a jiggle. Just tap the "x" on the apps you want to close down. It defeats the purpose of multi-tasking, but some apps do consume more battery, so it's a good idea to keep those that are open to a minimum.
We have a iPad 1 and it's mainly used for mail, internet and video and get's pretty heavy useage on evenings and weekends. We definitely get the 10 hours out of it.
I've not heard of too many issues with battery failure so I can only guess at either iOS5 or heavy app useage at this point.