How do I know when my power bank is charged?

[AC Question]

I was given a free power bank and it has no power buttons or any other buttons. When I plug it into the USB port on my computer it lights up either red or blue where the plug goes in. I don't know what the red and blue lights mean. Sometimes it's red, sometimes blue, sometimes it fluctuates back and forth between red and blue when I move it. How do I know when it is charged and how much charge is left?

 

[B. Diddy]

Welcome to Android Central! There's no way to be sure, since it sounds like some generic item. Red probably means it isn't fully charged, and blue means it's fully charged. The fluctuation might just have to do with a loose connection.