If you are using more than one battery in a circuit how should they be connected?

When using more than one battery in a circuit, they can be connected in series or parallel, depending on the desired voltage and capacity. In a series connection, the voltages of the batteries add up, while the capacity remains the same. In a parallel connection, the voltage remains the same, but the capacities add up, allowing for longer usage times. It's important to ensure that the batteries are of the same type and charge level to avoid issues.