What I learned with building the first iPhone charger shown above using 8AA batteries to get a 12v supply and then using a car adapter to regulate current and voltage and the iPhone 3 and 4.

Car chargers are not all equal in their design but basically cars when running show slightly above 14v and at least 12v when not running. The chargers are designed around 12 to 25v. The iPhone 3 was less critical than the 4 with several chargers I tried to low voltage input. Around 9v input was when I would get error messages from the phone. When I went to the i4 is when I started looking for a better setup and found the second one shown. It had the advantage of using re-charge batteries and also doubled as a charger with pass thru that lets you charge batteries and phone at the same time. The output charging amps is too low to do both the phone and the Mophie at the same time though. It works but got a little warmer than I liked and in reading the specs I saw I was pushing the limits. The fact it takes both types of batteries (throwaways and re-charge) makes it a nice fit for touring. I normally use it with re-charge and in a pinch can find throwaways everywhere. An added bonus is it works great with a little USB light also, handy when patching a tube in the dark or to light up a tent.

My Mophie is the newer higher capacity but not the weather resistant one. I don’t care to view my phone anymore like the setup I show in the first photo. I keep it handy in my bar bag but don’t need it in my vision all the time.