Check out this cool concept from designers Sungwoo Park and Sunhee Kim, the Energy Seed.
The Energy Seed is a bin for batteries, with a light on the top, the idea is that people put their old batteries into the Energy Seed and it then uses the left over power in them to power the light.
It is designed to take every type of battery and as you can see from the photo there are different sizes of holes.
This is a great concept and a cool way to use left over power, I am not sure how good it would be in practice thought, but it is great to see up and coming designers thinking about ways to save power and uses redundant energy to power every day items.
via Yanko Design