What is the effect of changing the numbers of batteries in a circuit?

Before we can attempt an answer to that question, we'll need to agree on the

meaning of the fuzzy, slippery phrase "amount of electricity". I'm going to interpret

that phrase to mean the current through the circuit.

If the batteries are connected in series, then more batteries produce more current

through the circuit.

If the batteries are connected in parallel, then the number of them has no effect

on the magnitude of current through the circuit. But whatever the current is, more

batteries will cause it to flow in the circuit for a longer time, before they run down.