Why is a 6 volt battery larger than a 9 volt battery?

Answer 1

i say nine volts are good for moters and six volt are good for emergency lighting.

Answer 2

Usually 6 Volt batteries are used for larger appliances and have more "juice" to carry out for long periods of time. While a 9 volt is tiny, it's not used for something that would use a lot of power at once.