can a battery be tested when the cars turned off

[CarmenRose]

Yes, you can and absolutely should test a car battery when the car is turned off. In fact, testing with the engine off is the standard method for checking the battery's health and state of charge itself, separate from the charging system. The most common and accessible tool for this is a digital multimeter.

Set your multimeter to the DC voltage setting (usually marked with a "V" and a straight line). Connect the red probe to the battery's positive terminal (+) and the black probe to the negative terminal (-). A reading of 12.6 volts or higher indicates a fully charged battery. A reading between 12.4 and 12.6 volts means it's at about 75% charge and is acceptable. If the voltage drops to 12.0 volts or below, the battery is only about 25% charged and likely needs to be recharged or may be failing.

For a more comprehensive health check, a load test is required. This test, often performed with a specialized carbon pile or advanced digital tester, applies a simulated electrical load (similar to starting the engine) to the battery while monitoring its voltage. A healthy battery should maintain a voltage above approximately 9.6 volts under load for a specified period (e.g., 15 seconds). A significant voltage drop indicates the battery can no longer hold a charge under demand and should be replaced.

Battery State of Charge	Open-Circuit Voltage (Engine Off)	Recommendation
100% Charged	12.6V - 12.8V	Battery is in good condition.
75% Charged	12.4V - 12.6V	Acceptable, but monitor if it drops further.
50% Charged	12.0V - 12.4V	Battery needs charging as soon as possible.
25% Charged	11.7V - 12.0V	Battery is deeply discharged; may be damaged.
Discharged	Below 11.7V	Battery is likely sulfated and needs replacement.

Testing the battery while the engine is running checks the alternator's output, which should be between 13.7 and 14.7 volts. Always prioritize a static (engine-off) test to diagnose the battery's core health first.

[LeEleanor]

Sure can. Grab a cheap multimeter from any auto parts store. With the car completely off, touch the red probe to the positive battery terminal and the black to the negative. If it reads around 12.6 volts, you're golden. If it's down near 12.0 or lower, that's your problem right there. It’s the easiest first step before you call for a jump or buy a new battery.

[StOmar]

Absolutely. As a technician, the only way to get a true assessment of the battery's state of charge and health is with the vehicle off and the key out of the ignition. We perform an open-circuit voltage test first. If that's low, we proceed to a load test, which simulates the massive draw of the starter motor. A healthy battery must maintain a stable voltage under that stress. Testing while the engine is running only tells us about the alternator's performance.

[OJasper]

I learned this the hard way after my old sedan left me stranded. Now, at the first sign of a slow crank, I test the battery with the car off. A simple voltage check takes two minutes. It gives me peace of mind to know if the issue is just a weak battery or something more complicated with the charging system. It’s a basic piece of diagnostic info that every driver should know how to get.