There are many of these on eBay as well, my question isn't where to find them, but which type of battery is best. Some use one 9-volt, some use 4 AA, some use 8 AA and I've heard of some using AAA. What I am trying to find out is if all of these fully charge an iPod. If I went with, say, the 9-volt, would the one work, or would I just need to use 4 9-volts seperately? If one 9-volt battery is effective, then it's obviously better for travel to carry one 9v than carrying 4 or 8 AA batteries for each charge.