Have a look at the Lenovo Yoga Tab models. I have an older 10" model that runs Windows, but there the majority are Android.

These have 2 main advantages for planes - the first is that they have a built-in stand, which works great on a tray table, but on many planes can hang somewhere on the seat in front of you (eg, it sits perfectly in the magazine holder on some of the new slim-line seats!)

The second is the battery life. Mine claims 12 hours, and when it was new I've pushed it to more than that whilst watching video. Even now (3 years old) I can get >8 hours of video play out of it.