Quote Originally Posted by Archerfish View Post
From the other thread about battery, I asked if is possible to just use a multimeter to check the battery health instead of a hygrometer.

Upon searching about this battery tester, I saw a video explaining​ how to use a voltmeter to check how healthy your battery is. It said that normally, voltmeter reading will be 12 and once you crank your engine it will read below 12. You should not have a reading below 10 volts while starting the car. Below 10 means your battery is about to "give up". Once the engine is running, you should have a reading of about 13-14 volts.

My question now is, how can you check the battery without cranking the engine and by using only a multimeter? Is this even possible?
yes and no.

you have to challenge the battery's ability to give out a heavy current. cranking does that. they even ask you to turn on all your headlights and aircon.

if you check the battery without challenging it, you will probably still get a 12 volt reading, even if the battery will die the next day.

with the engine running, you are now measuring the alternator's output, which is 13-14 volts. you are not measuring the battery's output.
they also test this, because, in many instances, the battery is dying because the alternator is defective.

yes, it is possible to check a battery that is not even connected to the car.
in older shops, the gadget they use has a large resistance wire that glows lightly, mimicking the starter's high current drain.
i am assuming, electronic instruments that do not glow hot in the dark, can do this. i used to have a cigarette lighter meter, that warns me of my battery's condition.

i'm eager to hear from kim. i am more historical. he is more up to date.