I simply had to register to inform you about what may be the best £1.99 you've ever spent!
They take just one AAA and have built-in electronics to hike the 1.5V up to the 3+ that the very bright white L.E.D. uses. The battery lasts for ages. They're also waterproof!
I've bought several of these to give away and keep - I may buy more because they're such a bargain! When you get yours, let us know what you think.
B.T.W., I have no connection whatsoever with the vendors!