The article above talks about the importance of battery life in phones, saying that many phones nowadays make the mistake of sacrificing battery life for thinness and lightness.
I actually don't think battery life is important. So long as the device lasts for one day, there is no need to worry. Most people charge overnight as a daily habit and don't think about it.
The iPad 3, with 11,000 mAh battery capacity, will last a long time, but it is too big. Your arms will get sore carrying it around for too long. The Nexus 7, however, is thin, small, and light, and it lasts long enough.