How to use a multimeter?

[AnthonyA1234]

From what I understand you let the headlights run for 3 min with the car off, turn off the headlights, and then you check the battery and it should not be under 12 volts. Then you start the car and it should not drop under 10 volts. Is this correct?

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[NGOT8R]

If your car battery is dropping below 10V at any time, I would suspect that you have a bad battery. One other test you could do when the car is running is, disconnect the battery to see if the alternator carries the load. If it does, that would also be an indicator of a battery that may no longer hold a charge. I have run my battery down below 12V listening to the stereo, but put it on a 10A battery charger to recharge it and it successfully takes the charge.

 

[NGOT8R]

FYY, my fully charged battery reads between 12.9 and 13.2. This is in a 2019 Bullitt.

 

[AnthonyA1234]

Ok sounds good. When driving around the voltage meter in the cars gauge cluster display says 12v is that a sign of a bad battery?

 

[AnthonyA1234]

FYY, my fully charged battery reads between 12.9 and 13.2. This is in a 2019 Bullitt.

With a multimeter? Or the cars gauge cluster meter

 

[NGOT8R]

No. You should be fine. My car has been on a battery charger (fully charged and trickle charging) for several days. Here is what it is reading at this very moment.

 

[AnthonyA1234]

No. You should be fine. My car has been on a battery charger (fully charged and trickle charging) for several days. Here is what it is reading at this very moment.

That’s while the car is off correct?

 

[NGOT8R]

With a multimeter? Or the cars gauge cluster meter

With a multimeter.

 

[NGOT8R]

That’s while the car is off correct?

Yes.

 

[AnthonyA1234]

My situation is that about a week ago my battery died after I didn’t drive it for a weekend so I recharged it but then the next morning it didn’t start so I replaced it with an interstate battery. Then the next weekend I didn’t drive it again and that battery died. The only mods I have done to the car that involves anything electrical is reupholster my steering wheel which involved me taking it off and putting it back on. I also have a anti theft tracker in my cars OBD port which I removed because I assumed it has to be that. So I recharged the interstate battery and have been driving it the past few days to work and it has had no starting issues however the voltage meter in the gauge cluster reads 12v which I’ve never seen before it’s usually 13.5-14v. That’s why now I want to test this battery with the multimeter.

 

[NGOT8R]

Are your drives really short drives? Usually, an hour drive or longer (preferably on the interstate) is the best way to allow the battery to charge to it’s full potential. Short drives won’t cut it. Are you charging the battery at home with a tender or actual battery charger? A tender will charge a battery, but will take a very long time to do it (as much as a few days depending on how low the voltage gets). I use a 10A charger and when my battery was 11.XX volts, it took 3 hours to charge it fully. Now I leave it on the charger until I am able to drive it.

 

[AnthonyA1234]

Yea my drives are usually pretty short about 20 minutes there and back. What do you recommend I do then?

 

[NGOT8R]

Try performing the test that I mentioned in post #2 to see if the alternator can carry the load. If it does, then I would turn the car off, reconnect the battery and go for about an hour long drive on the interstate.

Short of that, it sounds like something is stealing power when you think the car is off, such as a stereo amplifier or other device that is operating on constant 12V power instead of a switched 12V source.

 

[NGOT8R]

Try and keep the RPMs up while driving (maybe drive in 3rd or 4th gear), so that the alternator can put out more power to charge the battery. Keep an eye on the car’s VM gauge and you may see the needle climb slightly.

 

[AnthonyA1234]

How would I do that test I just disconnect the battery while the cars running and see if the alternator can keep it running?

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