Dig into notifications. See what you may have on that you don't realize. See how your e-mail is set, if it's on push or fetch. I believe on Push it reaches out to get new mail regularly, which will drain your battery.
Chances are you have stuff running in the background that you dont' even realize that's draining the battery.
Also if you have wifi sync enabled and on and your comptuer on with iTunes open and active, your iPad could be reaching out to sync continually and you don't even realize it.
I agree with Skydiver119's suggestions, but consider the fact that if your iPad is the original version, and it could be coming up on two years old, it is possible that the battery could be starting to die on you. I am not stating that this is absolutely the case, I am merely suggesting that it is possible.
I would then recommend NOT letting it go two days without charging it. I charge my iPad every single night. Maybe it sounds like a PITA to charge it every night, but if the battery is slowly dying, why would you want to take a chance?
Consider this as well, if you haven't radically changed the way you have been using the iPad and the battery is draining, then that might be evidence that the battery is going. What I mean is that if you never had Push turned on or if you don't have battery draining things going on in the background and never did, it would seem to be more evidence that the battery has started to go on you.
Take Skydivers advice and see what happens. I don't mean to be a gloom and doomer, but at some point, the battery has to go on these things, they were not built to last forever.
Look at the Extend iPad Battery Life link (below) first.
The quickest way (and really the only way) to charge your iPad is with the included 10W USB Power Adapter. iPad will also charge, although more slowly, when attached to a computer with a high-power USB port (many recent Mac computers) or with an iPhone Power Adapter (5W). When attached to a computer via a standard USB port (most PCs or older Mac computers) iPad will charge very slowly (but iPad indicates not charging). Make sure your computer is on while charging iPad via USB. If iPad is connected to a computer that’s turned off or is in sleep or standby mode, the iPad battery will continue to drain.
Apple recommends that once a month you let the iPad fully discharge & then recharge to 100%.
How to Calibrate Your Mac, iPhone, or iPad Battery
At this link http://www.tomshardware.com/reviews/galaxy-tab-android-tablet,3014-11.html , tests show that the iPad 2 battery (25 watt-hours) will charge to 90% in 3 hours 1 minute. It will charge to 100% in 4 hours 2 minutes. The new iPad has a larger capacity battery (42 watt-hours), so using the 10W charger will obviously take longer. If you are using your iPad while charging, it will take even longer. It's best to turn your new iPad OFF and charge over night. Also look at The iPad's charging challenge explained http://www.macworld.com/article/1150356/ipadcharging.html
Also, if you have a 3rd generation iPad, look at
Apple: iPad Battery Nothing to Get Charged Up About
Apple Explains New iPad's Continued Charging Beyond 100% Battery Level
New iPad Takes Much Longer to Charge Than iPad 2
Apple Batteries - iPad http://www.apple.com/batteries/ipad.html
Extend iPad Battery Life (Look at pjl123 comment)
New iPad Slow to Recharge, Barely Charges During Use
Tips About Charging for New iPad 3
Prolong battery lifespan for iPad / iPad 2 / iPad 3: charging tips