Lepow Official via Amazon offers Prime members the Lepow Moonstone 6,000mAh External Battery in Apple Green or Glossy Black for $21.99. Apply coupon code "D6PPNAQ6" to cut the price to $17.99. With free shipping, that's the lowest total price we could find by $12 for this battery in any condition, although we saw it for $2 less last month. (Non-members can spend $35 to qualify for free shipping; otherwise, shipping adds $5.37.) It features two USB ports and is compatible with most smartphones and tablets.