More on electricity

Do all boys love to play with batteries, electricity, circuits etc? I know that my boy does.
He is obsessed with batteries - in his room, on his desk, among the books you will find batteries, all kids of batteries.
He knows that to run his train set on full speed he needs a set of "fresh" batteries and that he doesn't need very strong batteries for a TV remote. He checks how much "juice" is left in the batteries and marks them accordingly (puts little stickers on the ones that can be used, for example, only in remotes).
This semester we are doing some experiments with electricity and circuits. This is what we created before we left Taiwan:

Light is ON ...

and light is OFF.