I charged mine to 100% left wifi and bluetooth on, cellular off. It was still 100% after 24 hours of no use just sleeping, after 48 hours is 99%...will check after another 24.
When I was using it, was getting 11 hours on a "full" charge...my brightness is set at 40% no auto, LTE off, using just the wifi. I better hold on to this one, sounds like I won the battery lottery.

Easily as good as the 2nd gen. I have maybe better.
Still have my iPad 2, so I could afford to let the new one sleep to test it, wanted to see if the new one lost anything just sleeping and I guess in my case it's like the 2, hardly loses anything in sleep.
I find WIFI or the new bluetooth does not effect my battery while sleeping, things that will lower battery while sleeping...push email (don't use push on my ipad) iCloud sync? And other apps that check the internet while left in multi task mode, some apps ask you if you want push notifications.
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How to turn off the "radio" to save my battery? Thank you.
Settings, cellular data...turn off when not using and on wifi...this can be huge depending on how strong your cellular signal is, the lower the strength (if your far from a tower) the more power your device may use.