Anker PowerCore 5000 Battery Pack | $17 | Amazon
Photo: Anker
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Anker makes a lot of really big battery packs. You probably own one or two of them. But it’s also worth keeping a pocket-friendly one in your arsenal for days when you need some extra juice, but don’t want to carry a bag. This 5,000mAh model can fully recharge basically any smartphone at least once, and it’s only $17 right now, down from the usual $22.