Batteries are a very handy source of power.
Just think of all the things that use them - calculators, cassette players, even computers will run on batteries. You'll know that there are different kinds of batteries, and maybe that some are good for some jobs, and some for others. But battery power is expensive. It would be really good to know which batteries are best for certain jobs. For a first experiment, I wanted to see if batteries were different, so I tested two to destruction - I left them to power two lamps until they were used up.