I reviewed the mophie juice pack air case for my iPhone 5 recently, and I liked it a lot. If you’d prefer to use your iPhone case-less but want to keep a backup power source at hand, you should check out mophie’s power reserve. mophie packs 1350mAh of reserve power in a package only 1.50″ X 2.84″ X 0.56″ and weighing about 2 ounces. It’s the perfect size for a keychain fob, and it even comes complete with a key ring. There’s a Lightning cable built in, so you have everything you need to give your iPhone or iPod a power infusion (up to 50% additional). It’s available to ship now in black; white and red versions will be available later this month (April 2014). The mophie power reserve is $49.95.