The 42.5 watt-hour battery mentioned in the official iPad specifications above is a big honking battery for such a thin and light tablet. It's clear the same battery is being used in both the Wi-Fi and Wi-Fi + 4G models, as indicated in the two columns of the specs above.
The 10 hours of the Wi-Fi only iPad is in line with the run time of the current iPad 2, which is no surprise. What is a surprise is why there is only a one hour run time difference indicated by Apple for Wi-Fi and LTE operation. I have tested LTE operation on at least a dozen smartphones and two tablets, and the 4G technology has used significantly greater power than Wi-Fi in every case.
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In my extended testing using LTE on a 10.1-inch tablet, the battery drain compared to Wi-Fi operation was noticeably faster, at a rate of nearly 2-to-1. The tablet would run 10 hours on Wi-Fi, and perhaps 5 hours on LTE connectivity.
My experience with LTE proves how significant the 9 hours of run time that Apple is providing with the new iPad. This is a tremendous achievement, and probably the most significant improvement over the iPad 2. This upgrade makes it all the more confusing why Wi-Fi operation isn't better than older models of the iPad. I would expect a near doubling of run time on Wi-Fi over LTE, even with the Retina Display.
Either Apple has implemented a totally new LTE radio that is very battery friendly, the Wi-Fi only iPad has a different battery than the 4G model, or there is some other mysterious difference present in the two models. I can't wait for the standard breakdown of the new iPad models once shipping to see what is going on inside the slate.