I have a couple of those external batteries you can use to charge up cell phones and other portable devices. I got this one, and we have others that are pretty much the same.
Both of mine, and all of the others I have seen, have a standard size USB jack for the output side and a micro USB on the input side for recharging. They generally come with a short cable with plugs of those types at each end.
Ever since I got the first one a couple of years ago, I have wondered what would happen if I plugged the output into the input. It’s like that urge to jump that some people have when standing at the edge of a cliff, or like this.
To anyone with even a slight knowledge of electricity it’s clearly a terrible idea. But there’s nothing physically to stop you from doing it, and there are plenty of total idiots out there (obviously!). So shortly after I realized it *could *be done, I tried to reassure myself that there must be some sort of built-in circuitry that would prevent a disaster if someone actually did it.
But I haven’t tested it to see if I’m right. Does anyone know?