Battery Pack for iPod Nano

Is there a difference between the voltage that a Nano uses and the voltage of other iPods? Could you, as an example, use the firewire sync/charge cable from other iPods to charge the Nano? If you can, and the voltages are compatible, why couldn't you use a battery pack for another iPod with the Nano?

Well, I went down to my local WestWorld today to get some "official" help on this issue since it seems that no one from Apple ever reads or responds to posts here.

According to the techs at WestWorld there is no difference in the charging voltage between USB and Firewire. As such, any battery pack currently on the market that charges via the dock port will be compatible with the iPod Nano.

That's for a Shuffle. I'm talking about the Nano.

Won't be released until March. =(

Belkin TunePower

Energizer ER-i50 iPod Battery & Carrying Case

Griffin TuneJuice Battery Backup for iPod and iPod mini

There's more out there but these are the one's that I know of.

See also:

Tekkeon myPower for iPod MP1100.

NYKO iBoost for iPod

NYKO iBoost Mini for iPod

This one is amazing if it lives up to the company's promises:
iCel for iPod