Ipad2 battery life
I've noticed about 10 to 12% an hour on my 3G 32gb iPad2. That was on wifi, more like 8 to 10% loss an hour on 3G. That's with my screen on 50% brightness. I have noticed that my iPad2 screen on 50% brightness is almost identical to my iPad 1st gen on 100% brightness, maybe just a little dimmer. But if you consider the 10 hour battery life Apple claims then somewhere between an 8% and 12% loss an hour would make sense.
I would suggest a full discharge and a full charge to your battery to see if that would remedy your problem. That helped me in the past with my 1st gen iPad if I felt like it was losing charge to quickly. Also,
eBay has various portable batteries for a decent price (I don't recommend off brands, they may claim to charge iPad but the may not, I had that problem). I bought a Cinch charger for around 30 bucks and I ordered an extra iPad cable since Cinch said the one included wouldn't work with iPad. I have been really pleased with it, I keep it my bag with the extra cord and I don't worry about running out of power. I hardly ever use it but still worth the 30$. It works with my iPhone 4 as well. Oh and it's 5500mAh I think. I hope this helped