Series Connection: This involves connecting the positive terminal of one battery to the negative terminal of the next.
Voltages add together, but the capacity (Ah) remains the same as a single battery. For example, two 1.5V batteries in series provide 3V.
Parallel Connection: This involves connecting all positive terminals together and all negative terminals together.
Voltage stays the same, but the capacity adds together, allowing the device to run for a longer period.