Unifun via Amazon offers the Unifun 10,400mAh Waterproof Portable Battery Pack, model no. U821, for $16.99. Coupon code "7KYUNRJU" drops it to $13.49. Plus, Prime members bag free shipping. (Non-members can spend $49 or more to qualify for free shipping; otherwise, shipping costs $6.74.) That's about a buck under our mention from two weeks ago and the lowest total price we could find by $6. It features a waterproof rating of IP66, dual USB outputs, LED flashlight, and LED power status indicator. Deal ends January 31.