If you find your self stuck with lots of tools and gadgets that run on AA size batteries then you might want to consider having one of these, the USBCell. Not different than standard AA batteries, the USBCell works the same way. The only difference is that it can be charged via any USB port that is of course powered ON.
Just remove the top cap and plug it into a USB port for charging. Normal charging time is up to 4 hours. The cell also contains and LED for indicating charging status. No need to pay extra for a battery charger if you have the USBCell. The USB cell can also be charged via standard battery chargers.
You can easily get this USBCell for less than £13.