What is system voltage?

since this is posted under cars and vehicles I'm guessing by "system" you mean car systems, battery voltage when the car is not running is 12.6 DC volts, car batteries have 6 cells 2.1volts each. (lots of people think its 12v which is not true) When the car is running and the alternator is charging the battery, it varies but usually between 13.2-13.8volts depending on electrical load, battery charge before starting the car etc etc... hope this is the answer you were looking for.