For Prime members, zweiyu via Amazon offers the Dual-USB Output 5,000mAh Rechargeable External Battery in White for $19.99 with free shipping. (Non-members can pad their orders over $25 for free shipping; otherwise, shipping adds $5.31.) That's $2 under last month's mention and the lowest total price we could find in any color by $4. It functions as an emergency backup power source for cell phones, tablets, and other devices. It includes adapters for Apple, Samsung, Motorola, and more.

Amazon Prime membership is $79 per year; however, Prime is free for college students for six months, and free for parents and caregivers for three months.