Hi again, Nancy,
Yes, if you can charge your iPhone through the 12v power receptacle in your car here in the U.S., you can do the same thing in Scotland. Your hired car will have a 12 volt battery, and a power receptacle/cigarette lighter. Also, hired cars now have a USB port. We found this out to our dismay in June when we picked up our hired car. It didn't have a CD player, only a USB port, and we purchased over 80 CDs along the way, with nothing to play them on! :( We were stuck for 30 days listening mostly to Radio One, which is horrendously awful! It's just about all you can pick up as you get farther north. Once in a while we'd pick up a low wattage local radio signal, such as Isles FM or Mearns Radio, but it would soon fade out as we got farther away from the transmitter.
BBC Scotland was good on occasion, especially late at night, and there was a lot of good music on BBC Radio nan Gaidheal, but much as I hate to say it, the music on BBC Radio One is chalkboard gratingly awful!
Even though you can charge your iPhone in the car, you should still get an adapter for the days that you don't have a car.
One month to go!