Anyone who has taken introductory physics will recognize this famous question:

Why can't you start your car with 8 AAA batteries instead of one 12 volt car battery?

Eight AAA batteries do add up to 12 volts, but they still can't provide enough electrical current to run the starter motor. But that's not the whole story. Any battery has a limit on the maximum current it can produce.

To explain why, I'll make a model to represent a real battery.

The pair of vertical long-short lines (labeled V0;) right of center represent the ideal battery. Or, in other words, how much current the real battery would produce if it wasn't confounded by resistance (represented by the squiggly line labeled Ri). Yes, all of this ideal battery/confounding resistance stuff is going on inside the actual battery.