We all know how battery testers work: you find a battery in your home or office and have no clue if it's still usable. You attach it to a battery tester and voila - the battery is flat so you can happily dispose of it. But on washing day, what are you to do if you find a couple of stray socks? Sure, you can smell every single one of them, but that isn't only unpleasant, but it can actually damage your health, e.g. if you're allergic to dust. Alternatively, you can throw everything you...