I don't really like batteries because I don't like the hassle of having to change them and going to the store to buy more. I had an old wireless mouse using two AA batteries. I never use it because I never have the batteries for it. I did an experiment and connected the two terminals to a 5V USB powered port and the mouse works. Obviously, I did not care about the mouse, so I was willing to experiment. I'm wondering what's the level of tolerance for those kind of electronics in general? Will all electric devices that take two AA or AAA batteries work fine with USB power?