We spent 15 hours researching nearly 30 USB battery packs, eliminating models that were either too expensive, too bulky, or too short on storage. We settled on 5 finalists based on their ratios of size, weight, and cost compared to the advertised capacity. We then had an electrical engineer spend almost 245 hours testing these finalists in order to find that the $30 IntoCircuit Power Castle 11,200 mAh is the USB power bank that most travelers should carry in their bags or briefcases. Little touches like an LCD that displays the remaining charge by percentage and automatically starting to charge devices you plug in without a button press make it feel more thoughtfully designed than the competition. It’s also the battery pack that held the most mAh per dollar.