Belkin BOOST CHARGE 3 Port Power Bank 20K

The BoostCharge Power Bank 20K provides your USB devices with up to 20,000mAh of power, or in real terms up to a theoretical max of 78 hours of extra battery life for compatible iPhones and other USB devices. There is a visible 4-dot battery indicator on the side of the unit, and this did take a long time to charge fully. I started charging it using a USB-A to USB-C cable and after 8 hours at work it was only half full. Switching to a powered USB-C cable charged it the rest of the way in a couple more hours.