Thread: What specific voltage do you read for the battery with the engine off?

I've got what might be an over-active alternator, or a battery that is too powerful. I want to know what other people have for voltage across their battery terminals while the engine is not running. It doesn't matter if it's an SR20 or even a Nissan. Just any old car will do. Just throw numbers at me from your readings in the past or go check your car for me when you get a chance. Accuracy down the the tenths of a volts at least is what I'm looking for.

If you know your battery is dying, I don't need your data. =D

12.6 on the b13

Thanks for the help man.
Keep'm coming people.

What voltage should a car battery be at? - Club Lexus Forums



CAR BATTERIES ARE NOT 12 VOLTS

The battery in this car is 13.65 volts with the engine off. I'm starting to think it is what killed the airbag controller and ECU and blew untold number of fuses.

Or could it be the alternator over-charging the system? Will a "good" battery even get up to 13.5 volts with an unregulated alternator?

Mine tested 12.52v. Don't know how accurate the scangauge's reading is but it ranges between 14.0v - 14.7v when it's running... I'm not sure if a battery will overcharge like that, maybe it IS bad? I'm not sure 13.65 volts would blow stuff though since it runs at 14+ with the engine running, maybe wildly fluctuating voltages from a bad voltage regulator would fry stuff...? idk

edit: that 12.52 is from dvm not the scangauge

Engine off, as above, 12.6volts is good. If you've got over that, its likely the battery has been over charged or you should let it settle for a bit longer as the battery voltage will remain high for a short time after the car is switched off until it settles (mine does anyways).

Over 15 volts is bad and says the alternator regulator is bad and will cause the battery light on the dash to come on along with the handbrake light (i think that happens at 15.2v).

MOST of the components in the car can withstand small spikes and peaks in the voltage, but i've seen alternators with a bad reg putting out 16 and 17 volts which will seriously fry stuff.

where did you buy the battery from?

wow i've never seen that high. the way batteries work should not allow them to be that high, even if overcharged

A battery is 12V nominal. That means it has 6 cells that will have 2 volts each. Now there is more to that. You dont charge a battery to 12V and leave it at that. You charge to about 2.4V per cell or 14.4V. If you over charge a battery it will hold a "surface charge" for a little while but eventually bleed down to its at rest voltage which is around 2.1VPC or 12.6V on a fully charged battery. Each battery is different but that is the general idea. If a cell starts to fail you will have less voltage and not more. You can not create more plates or cells in your battery.

I would say the alternator is junk and it could cause damage to the battery if over charged too much.