Rechargeable batteries are great in theory. You never run out of batteries, because they're always there, ready to be juiced up and used again. In theory. And though they're more expensive to buy, you'll use them again and again, thus saving yourself a fortune. In theory. In practice, you have a large pile of batteries you forget to charge, so when you need them, you'll have to wait a couple of hours for them to get enough power. So you end up buying regular batteries anyway, because rechargeables require forward planning. But the Batteriser could be an option. According to the people behind the stainless-steel sleeve, most of your single-use batteries are thrown away with some power still in them. The Batteriser uses proprietary technology to unlock that extra power. Currently on preorder, for delivery in 2016. batteriser.com