Joe, you might also consider a wall charger. I have the KabelDirect wall charger, which I bought from Amazon for $15.99.
I don't have an iphone, but this can be used to charge that, plus pretty much any other device. IOW, you can lend it (plus a cable) to friends with iphones, and you can use it yourself for your phone. I use mine to charge my cheapo tablet, my phone, my mp3 player, my portable battery packs, etc.
I've purchased a few inexpensive ones on Amazon and I will say that they don't always last very long. I even received one that didn't work at all upon arrival that cost $7.99. Luckily, Amazon has a decent return policy.