How to use 3rd Party chargers with iPhone?

I'm going to Download festival in a few weeks and camping for 5 days, obviously, my iPhone 5 battery will barely last the first day, even being careful, so I bought a cheap AA battery powered portable charger to get me through. However, since apple have placed restrictions on what you can use to charge their products, when I plug it in, it says 'This accessory may not be supported' and no longer lets me charge it. Does anyone know a way to bypass this? Thank you so much!

Oh and before anyone uses this as an excuse for a rant, yes I know its probably not in my best interests to take an iPhone to a festival, but I want it to take photos on and also to call home as I'm only 16 and travelling a few hundred miles to the festival. If I took a different camera, it would still be around the same price to replace as my iPhone, so I lose in both options, and would rather pick the most convenient.

Use the Apple USB cable you would use at home, but in a different USB charger.

It's the 'Lightning' plug that fits the phone that has to be the genuine Apple bit, you can use any 5V USB source to connect the USB end of the cable to.

You can get rechargeable USB power units quite cheaply now, example:
http://www.ebay.co.uk/...1129491271

Something like that should charge your phone 3 - 4 times before it needs recharging itself - just make sure it's fully charged before you go…

For info, The lighting port is not a simple connector, it's more like an expansion data bus - any item connected to it has active electronics that the phone needs to 'talk to' to work out what it does and how to drive it - you can connect anything from a stereo audio interface to HDMI video to a memory card reader via that little socket.
If the phone (or ipad) does not recognise the connected item, it does not know how to use or control it.