As time passes, batteries become more space efficient, offering higher capacities in smaller packages. iWalk's Extreme 10,000 Duo ($100) is a good example of that. The long tube is quite narrow for a battery with a 10,000mAh capacity; the total volume is less than we'd expect. One mirrored edge houses 2.1A and 1A USB ports, and a micro-USB port charges the pack. It wouldn't be a modern day battery without a flashlight built in, too. Extreme 10,000…
