This is a very helpful guide for picking the sort of tablet you want to prepare for a disaster situation.
The interesting thing to note about the testing done is that they tested using a continuously running video file. Book reading may have a different effect on the battery life compared to playing a video.
The Apple iOS Devices are near the top in terms of playing video for an extended period of time. That is about expected since the Apple iOS devices are built to a relatively high standard of quality. The 64GB iPad Air with an Otterbox would be a great choice but you are going to pay through the nose ($780+) for something that still has less storage space than a comparable Android device.
The Samsung Galaxy Tablets are still good to go. Even though the battery life is not as high as some of the competitors, the ability to have a ruggedized case is important along with the ability to max out your storage space beyond 64GB.
I was very surprised that the Lenovo Yoga series performed as well as it did. My only gripe about the Lenovo Yoga series is that I do not know of a rugged case that will fit it and provide serious water and/or impact resistance and let me use it at the same time.