Hacking 'em batteries for a longer battery life
1. Turn C batteries into D batteries: Use three quarters (or similar), stacked on the positive end of the battery, so that the C battery is of the correct length. This temporarily costs you about $0.75 (or perhaps 15 or 30p?) per battery to hack, and you get your money back. It doesn't last nearly as long as real D batteries, but for short term fixes like getting your vibrator flashlight to work in a nuclear bunker during a swine flu pandemic, it might just save your bacon.
(A commenter on LifeHacker pointed out that you can substitute AA batteries for C batteries because they're the same length. There was somethig about using a 'PVC lawn sprinkler riser' to compensate for "the extra girth that C batteries have over AAs", but I speak no DIYglish).
2. Recharageable systems: Another tip that you've already heard is to get serious about rechargeable batteries, especially if you use high drain devices like digital cameras. A company called mahaenergy.com makes a good rechargeable system, and one reader from LH suggests that solar battery rechargers get a bad rap, suggesting that you should give them a try.
You can read the full list of hacks at Lifehacker.