OK, since I have had my iPad and iPhone, I have not had the chance to do a complete cross-country vacation. I have just gotten back from a trip to Sacramento and Napa California. the travel to and from took about 7 hours (that I could use my devices legally.) My test was twofold. First, how long could I use my iPad on the plane to watch movies and second, how well would my tethering work between my phone and tablet. Short answer to both – extremely well.
I had a simple gadget bag that consisted more of charging cables and portable battery packs than anything else. I had the Zagg Spark 2, a solar charger w/ built in battery, Mophie iPhone battery case and Twelve South Compass stand, headphones and appropriate cables.
My airplane experience was awesome. I had a 3.5 hour flight to Vegas and the battery was still at 85% when we had to shut off the devices. I had watch 2 movies and part of another. On the second flight, finished up a movie and watched a show via the airplane wifi (worked wonderfully) and when we shut down the devices again, I was at 65% battery. That was constant use, with the screen at 100%.
During the rest of the trip, I was able to keep everything charged up and ready to go. the tethering worked just as well out there as here and having both was great for touching up photos using the iPad that were shot on the iPhone. One thing I may add in the future is an Apple Airport Express so I can share wifi between the devices on the fly and get the photos uploaded to the Photostream quicker and without worrying about the hotel wifi cutting off after a certain undisclosed amount of data use. Sorry, you damned hotels, piss off and just offer the wifi gratis. It is a freaking commodity now.
The return trip on the airplanes were just as good as the ones heading out. There was plenty of battery to cover the 7 or so hours.
So, bottom line. Batteries were nice, but not needed on this trip. Next trip, gonna get a charger that will do both iPad and iPhone at the same time and only take one battery.