One of our best-tested portable power banks is now 57% off on Amazon. Mophie’s ultra-compact Powerstation Mini is one of the most travel-friendly models we’ve tested. Portable power banks, also known as portable battery banks, can help charge your devices on the go without an outlet. He’s been using the ultra-compact Powerstation Mini to and from the office, and appreciates the extra space it’s allowed. While the Powerstation Mini isn't designed to power larger devices, it’s a fantastic option for phones, earbuds, or your Apple Watch.