Because it does not lose any voltage across a load, as it would when connected to a load, the open circuit voltage of a voltage source indicates its entire voltage value, because the voltage does not share any of its voltage with a load. The battery on the left is not linked to anything. It has an open circuit, so it must be very close to full strength 12 volts before it will harm anything. The battery on the right has some resistance between itself and earth, so some of its power is lost as heat.
The Full Voltage of a Voltage Source is represented by Open Circuit Voltage. The term "open" in this case means no connection is made to the voltage source's terminals, so it can give all of its voltage to the load.
Open Circuit Voltage is also called Terminal Voltage or Short-Circuit Voltage. It is the voltage that a voltage source gives out when there is no connection made to any of its terminals. For example, if you connect a voltmeter to a battery without anything else connected, then the terminal on the voltmeter will read about 12 volts even though the volatge source is not being used at all. This is because that's what's left over after everything else has been used up. The same thing happens with other voltage sources, such as solar cells, power supplies, and batteries. They all have a full voltage value that can't be used because there is nothing connected to use it.
For example, if you have a 9-volt battery and connect one end of a light bulb to it, the other end will usually show about 6 volts because that's all the battery can give out before it is completely drained.
Without any load connected, we may measure the voltage of a battery across its terminals. This is referred to as the open-circuit voltage (VOC). Because no current flows through the internal resistor, the voltage drop across it is 0 V. Therefore, the battery has a open-circuit voltage of VOC.
The open-circuit voltage of a cell depends on its type. For example, a 1.5 V cell will have an open-circuit voltage of 1.5 V. Cells must be considered when calculating VOC because they have different minimum voltages required for operation. For example, a 1.5 V AA cell will not operate at completely empty, so its VOC will be higher than that of a 1.5 V AAA cell.
For standard cells, VOC can vary between 12 V and 20 V. For high-voltage cells, this range can be increased to 40 V or more. For example, a 48 V cell battery would have a maximum possible open-circuit voltage of 50 V. But since cells lose voltage over time, we would never actually see this value. The actual open-circuit voltage of such a cell is probably less than half of this value.
For batteries used in devices such as cameras and phones, the voltage applied to them is usually controlled by a circuit component called a "resistor".