As part of my preperations for WWDC I decided to get an external battery charger for my iPhone. I never actually ran out of power last year, but I got very close almost every day and I had to make an effort to keep it charged. I think it will be nice to have a charger available for emergencies. I looked on monoprice for their 30-pin compatible chargers and I found a few of them. But there are a lot of problems with these. For one thing, they're marked up on price compared to the USB options. For another, if you use a case you'll have to take it off to use them. I didn't want to deal with either of those issues, so I decided to combine parts to make my own.
Here's what I got:
That is a 2800 mAh battery, a USB 2.0 A Male to mini 5 pin Female adapter, and a USB 2.0 A Female to A Female coupler. What that let's you do is plug any Apple 30-pin cable into the battery to charge your devices.
I tested it out on my iPhone and it worked very well. It charged my phone from 50% to 100% in 1.5 hours and used about 3/4 of the battery's charge. I'll definitely be keeping this guy charged up and in my backpack all week long at dub dub.
Screenshot of shopping cart below: