This article was written by Thomas Opsomer Say you replaced your corded vacuum cleaner with a battery-powered one a few years ago. Initially you were thrilled with the convenience of not dragging a cord around, but by now the battery barely holds enough of a charge to make it to the other end of your living room. So, you pass by the store to ask about a new battery – only to learn that just the part costs about as much as a new vacuum and on top of that there will be labor costs, so it would mak...