Just Mobile's original Gum battery pack was a big deal when it debuted in 2008, offering one of the best price-to-capacity ratios we'd seen in rechargeable iPod battery packs. Since then, the company has introduced Gum Plus and Gum Max, which shared a more elegant, MacBook-inspired metal design. Now the company has brought the Plus and Max designs to a new version of Gum ($50), which has been upgraded internally as well. Still armed with a 2,200mAh…
