So, I'm planning to bring my iPhone 4 with me to a 4 day festival this year, and as we all know, the battery is never gonna last that long. There are charging stations at the festival but no way am I leaving my iPhone with some clown at a festival for a few hours. So, I want something I can use to charge my iPhone while I'm there. I've seen little devices on eBay that you can put two AA batteries into and then charge your iPhone off that. This sounds perfect. However, the ones on eBay sometimes mention that they'll work with a 3G, but not a 3GS. I can't find any that mention the iPhone 4. I thought they'd all just work as the little connector for iPhones/iPods seems to be standardised across all devices. So, anyone any idea where I can get a AA battery charger for an iPhone 4? For the record, I'm based in UK.