The battery (more correctly, the voltaic cell) is a convenient source of electrical energy. How batteries work will be discussed in more detail later. At this point, you can think of a battery much like a turbine pump. A battery provides a steady pumping action that circulates electricity around a circuit. A good analogy is an old canister-type vacuum cleaner. Such vacuum cleaners suck air in one end and blow it out the other. A battery pushes electricity out one terminal. After the electricity flows around the circuit, the battery sucks it back into the other terminal. When using the conventional current model, the high-pressure side of the battery is the positive side and the low-pressure side of a battery is the negative side. When two batteries are placed end to end, the voltages add together. So, if you place two 1.5 volt batteries end-to-end, you get a total of 3 volts. Four such batteries would give you 6 volts. For basic circuit analysis, batteries are assumed to be a perfect voltage source with no other characteristics. This means that a 6-volt battery will deliver 6 volts no matter what the conditions. In reality, as conditions change, the voltage of a battery changes. For now, this will be ignored. Different types of batteries and how they react to different conditions will be discussed in Batteries below.