Why are there different size of batteries when each has 1.5 volts?

Question

Example: All of the batteries ( AA, AAA, C, D) they all have 1.5 volts?

Answer 1

Battery capacity is usually measured in mA H. e.g a 100mAH will delivery 100mA for 1 hour or 10mA for 10 hours (at the rated voltage)

Bigger batteries tend to have a larger capacity - i.e. bigger mAH figure

Answer 2

there are small gadgets that are space dependents that's why as a standard batteries are made of different sizes to fit the requirements of these gadgets. Example, some people prefer bigger flashlights while other prefer penlights. The bulb of these flashlights are just the same which require two 1.5 v batteries each.

Answer 3

The larger the battery, the longer it will put out that nominal 1.5 volts.