The Mophie Juice Pack is the newest entry in the growing market of supplemental iPhone 3G batteries, and in my opinion, its the best of the bunch.

The iPhone 3G is fantastic, but lets face it – the battery needs help. I’ve tried a couple of other solutions, including the Brando iPower (clunky case, horrible speaker, decent battery) and the the stick-on-the-bottom kind (awkward), which both ‘get the job done’ of improving battery life, but both have their own drawbacks.

The Mophie Juice Pack does not have these drawbacks – its simple, its well-made, its elegant.

Just slide your iPhone into the sleeve, and your ready to go – the included mini-USB cable charges both the iPhone 3G and the Juice Pack itself (in that order), and your iPhone will use the Juice Pack before draining its own battery.

The mini-USB cable will also allow you to sync with iTunes, so theres no need to remove the pack.

Posting battery life specs with the Mophie Juice Pack is kind of pointless – battery life on the iPhone can vary so much based on the age of the iPhone 3G’s internal battery, local reception, and what you do with the phone.

All I know is that the Mophie Juice Pack has more than enough juice for me – I never have to worry about it dying over the course of a day or two.

The form factor is so small I don’t mind it at all, it actually makes the iPhone handle better when using it as a phone.