DIY external battery pack for 2G

[Ornryactor]

I recently found this attempt at an external battery charger pack for iPods (and this cleaner second attempt). I would really like to build something similar for use with my G2 Touch, but am concerned about the electrical specifications. Obviously these projects are from 4 years ago, and use a Firewire port. I was originally planning on just replacing the Firewire port with a USB port, but thought better of it. The design doesn't include any resistors or anything, and I don't want to fry my iPod's battery. I'm no electrical engineer, so I can't really decode what little information I've been able to find. (I even asked my neighbor, an electrical engineering student, and he didn't know.)

The only info I've been able to find is actually from a post on this forum on September 1:

Hello...

I just made myself a portable ipod charger using the instructions here. I havn't tried it on my iPod Touch, but it seems to work on my 1st Gen Nano...

What I want to know before using it on my touch is the safety factor.

It uses 4xAA (rechargable) batteries (each one is 1.2v and 1800mAh) connected in series. It then goes straight to the USB and into the iPod without any resistors or anything.

From my calculations, it won't blow up my iPod or anything, but I need reassurance. Also, it'd be nice to know how many charges I could get out of one set of batteries.

Also, the iPod Touch's battery is 900 mAh, and 3.7 volts, if that matters.

Thanks!

-Donald J

This guy's pack is different from the one I linked, but I can't tell if it's any better or worse. Obviously, AA batteries would be more convenient to purchase on the road, but I don't know how they compare to 9V in terms of voltage or amps or whatever.

Has anyone built a battery pack for a 2G Touch? I don't care if it's safe to use on any other devices; I'm fine with restricting it to my Touch as long as it's safe to use on that. I don't want to 'supercharge' my battery constantly and prematurely destroy its life cycle.

If anyone's already built one, I'd love to hear about it. I'd also appreciate any input from EE or computer hardware gurus that can provide electrical advice. My EE friend can build whatever circuits are needed (if any); I just need the info. Hopefully it can still fit in an Altoids tin...