Unifun via Amazon offers its Unifun 10,400mAh Waterproof Portable Battery Pack, model no. U821, for $16.99. Coupon code "NDMPIQD3" drops it to $13.49. Plus, Prime members bag free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, shipping costs $6.74.) That's tied with our mention from last month and the lowest total price we could find by $4. It features a waterproof rating of IP66, dual USB outputs, LED flashlight, and LED power status indicator.