What voltage and capacity will you achieve by connecting two 12 volts, 20 ampere-hour batteries in series?

When batteries are connected in series, the positive terminal of one battery is connected to the negative terminal of the next. In a series circuit, the voltages of the batteries add together, but the overall capacity (ampere-hours) remains the same as a single battery. Therefore, connecting two 12-volt, 20-ampere-hour batteries in series will produce 24 volts (12V + 12V) with a steady capacity of 20 ampere-hours. The 40-ampere-hour options are incorrect because capacity only increases when batteries are connected in parallel.