Cells in series

Connect cells in series — the + of one to the – of the next, like links in a chain — and their voltages add up. Two 1.5V AA cells in series make 3V; four make 6V. This is how a TV remote or flashlight reaches the voltage it needs from ordinary 1.5V cells.

For matched cells in series, voltages add while the amp-hour capacity is approximately that of one cell. Total stored energy in watt-hours increases. Runtime depends on the load and converter: at fixed power, more series cells can extend runtime, so amp-hours alone do not answer that question.

Visualise it as water tanks stacked vertically. Each tank adds its height to the total, so the pressure at the bottom (voltage) keeps climbing. But the pipe carrying the water is still the same width — the flow capacity doesn’t change.