Question

A car battery seems to be malfunctioning (not providing the proper voltage and current to start your car). While the car is off and you are not trying to start it, a friend uses a voltmeter to measure the voltage and finds that your battery voltage is 12.0 V, just as it is supposed to be. After the voltage check, you try to start your car again to no avail. Can you rule out the battery as the problem?

Answer 1

No. You cannot rule out the battery even after the open circuit voltage measurement. The open-circuit voltage may not have changed but the battery's internal resistance may have greatly increased.