We've reviewed plenty of external battery packs for Apple's portable devices in the past, but Powerbag's Instant Messenger ($180) -- just one product in the company's large lineup -- is among the first Dock Connector cable-equipped battery packs to be integrated into a bag. The nylon messenger-style bag is quite large, with dedicated pockets for up to a 17" MacBook Pro, iPad or iPad 2, as well as plenty of extras. What's most unique here is the 6,000mAh…
