Batteries are power supplies that generate a constant voltage. This voltage is expressed in VDC. On a schematic diagram, each long and short line pair on the battery symbol symbolizes one power cell within the battery.
Battery supply is a constant voltage, as was stated, but the voltage in the circuit will vary depending upon what that circuit is powering. The formula for determining voltage in a circuit is V = I X R, which stands for voltage equals current multiplied by resistance. This is a variation on Ohm’s law, one of the most fundamental laws in all of electronics.