Lepow via Amazon offers the LePow U-Stone Series 12,000mAh USB External Battery Pack in Stone Grey (pictured) or Khaki Brown for $39.99. Coupon code "TWTQVVNU" drops it to $32.99. With free shipping, that's $18 under our March mention and the lowest total price we could find now by $27. It's compatible with most smartphones and tablets.