It does not have a battery, so it will not charge. It charges batteries of other devices (batteries) or other batteries. For example, you use it to charge a battery pack during the day. When the sun goes down you connect the battery it charged to charge something, like a cell phone, to charge it up. You can also charge a phone (battery) with it while it is in the sunlight. 

Yes, even when it is cloudy, it works, though never as well as in direct sunlight. I used it for 2 weeks on a Philmont trip, and it kept my devices charged. I still recommend a power bank instead of a direct connection. They just work better. I changed up the power bank, and it provided all the power to the rest of my devices. My DJ OSMO Action and my inflation device.