You have two sets of rechargeable batteries from the same brand. Early morning when you were going out, you picked up one set of batteries thinking that this one was the fully charged set that you kept for later use. But alas, at the moment you want to use your battery on your gadget, you realize the set you left at home was the charged one. If you were using hungry batteries, this would have never happened with you. This battery looks and works like usual batteries except it gets thinner as it is discharging; making it easier to tell which one is empty. Aside from that, the convenience of taking out exhausted hungry batteries from a packed battery compartment is another unique feature that everyone will like.