USB battery pack
From experience, I know that I will spend a good 6 hours without access to a power source for my iphone.
So I was thinking of buying a battery pack.
On eBay I can buy a 1900MAh pack for the iphone4 for about 30$ (I won't order from China because I risk of not getting it in time).
Or I can buy a 4000MAh usb battery pack for 15$.
I'm not just leaning towards the usb battery pack because it's cheaper and bigger, but because my iPhone has a Otter Defender case which makes it hard to connect anything else than a cable into its port. The case is thick so it doesn't allow an object larger than a plug to connect. I had a bad experience with an iPhone speaker station :p
I'm not sure what experience people have with USB packs (not iphone). I know the iPhone is very finnicky in its power source for charging, so I'm worried the USB battery pack will not be accepted by the iPhone.
Any recommendations/experiences with generic USB battery packs in hooking it up to their iPhones?