Batteries provide portable electricity. Although they are available in many sizes, the basic battery cell only produces between 1.2 and 3.6 volts. It is actually linking these cells together that enables the production of larger and more powerful batteries. For example, a 12-volt car battery may contain six 2.0-volt cells joined in a way that adds their voltages to produce 12 volts total across the terminals. Understanding these rules of electricity enables you to link batteries and create your own customised power supply.
Divide the target voltage by the voltage of the batteries you intend to use. For example, to produce a 12-volt battery from 6-volt batteries, divide 12 by 6. The answer, two, is the number of 6-volt batteries required. If you used 1.5-volt batteries you would require eight of them.
Connect batteries in "series" to produce a battery with a higher voltage. Use battery clips and wire to link the positive terminal of the first battery to the negative terminal of the second. Repeat this system to link all the batteries.
Keep the connecting wires between the batteries as short as possible to minimise loss of voltage and current. Using short and thick wires is better than long or thin ones. Ohm's law states that voltage equals current multiplied by resistance so, by keeping the resistance low, you maximise the potential current from the battery.
A cord connected across the negative terminal of the first battery and the positive terminal of the final battery will now produce a 12-volt supply.
Reduce resistance between the batteries by keeping connections clean and firmly attached. Combining batteries wired in series with batteries wired in parallel will increase the voltage and the current capacity.
Always link batteries with similar characteristics. If you use disparate battery types, such as a 9-volt and two 1.5-volt batteries, the high-powered battery will attempt to charge the lower-powered ones, causing the entire chain to overheat, with the possibility of it exploding. Do not "short circuit" the battery, as doing so may cause an explosion, injury or death.