When your battery is fully charged, how many volts is your guage susposed to register while driving?

 

I'm not sure what it would be if it were FULLY charged, but most every car I've ever owned will register around 13.2-13.4 while cruising with assories on. Obviously if the battery is drained somewhat, it will be more in the range of 13.6-13.8 until it recharges
If the voltage regulator goes out, most will run in high 14's.
Now obviously I'm not an engineer, so you may want to wait until someone with more technical background answers; I'm just basing this on MANY years of observation.

 

A brand new fully charged battery normally reads 13.6 volts with a meter. Your car should charge somewhere close to this under no load and full battery but it will vary .5 volts either way.

 

When you are running and the battery has recovered from a startup and so on, typically you will see 13.8 to 14.3 on the DIC or hand held meter on the battery. If you are in heavy traffic, HVAC running, the DIC voltage will slowly drop since the alternator isn't putting out enough current to offset the loss for all the current drain sources. Usually, in those cases, it'll bottom out about 13.1 but you would need to get going pretty quick.

 

Actually that's 12.6 not 13.6.. A 12 volt battery is comprised of 6 cells with each cell representing 2.1 volts hence the 12.6 volts!

With all your accessories off you should see between 13.8-14.2 volts.

 

My 02 consistently runs at about 14.2 with a well charged battery.

 

The only way to tell the voltage of the battery is to turn the key to the "ON" position.. The car should not be running at all.. no accessories on either.. Then read the gauge/DIC.. It should read anywhere from 11.6-12.6 depending on the condition/age of the battery.. Mine is at 11.6 right now as we speak The reading you get when the car (alternator) is running is the voltage the alternator is putting out not what the voltage of the battery is.. The voltage of the battery should always be around 11.6-12-6 with the car off.. Its a 12 volt battery... not a 13 or 14 volt battery. The alternator has to put out from 13.0-14.4 volts to run the a/c,lights etc as well as maintain a positive charge on the battery to keep it within the 12 volt range.. My battery is 3 years old and probably close to the end of its life.. A strong healthy battery should maintain over 12 volts if driven on a daily basis. 11.3-11.5 is usually where you need a jump... The engine wont crank over.. Even after you get a jump from your buddy and drive away with the lights and a/c on the DIC is still going to read from 13.0-14.4 volts.. This is what the alternator is putting out.. However the bad battery no longer has the ability to store a full 12 volt charge... So the next time you start the car it may or may not start again... Generally the battery is shot or close to it...

 

Well said!!

 

Using a voltmeter accross the battery terminals at least 2 hours after driving or charging the battery, with no active drain, a 12-volt battery will measure at about 12.9 volts when it’s fully charged and about 11.4 volts when it is fully discharged.

It turns out that a fully charged 2-volt cell has a voltage of approximately 2.15 volts. Oddly enough, a fully discharged 2-volt cell has a voltage of 1.9 volts. That’s only a difference of 0.25 volts on each cell from fully charged to fully discharged.

A load test is the only real way to test a battery. Nearly anyplace that sells batteries will do one for free.

 

What does a "Load Test" actually do?

Is the "Load Applied" during this test the same for ALL cars?

I have a new Alternator, Starter, Battery, and Ignition switch installed and all seems well driving around, but when I have O'Reilly's do a Load Test it still shows "Alternator Output Low/Diodes OK" (same message I was getting prior to replacing all the parts)?

 

The "new alternator" concerns me.. Evil Twin or Bill Curlee can chime in on this.. I recall the alternator is made in France and not all aftermarket replacements are compatible.. Try a search or pm these guys for more info..

 

The load tester applies an actual amperage load to the battery, to simulate the starting current that the battery is rated to supply.

The load applied to the battery will vary. It's value is determined by the specific cranking amp. capacity of each battery. The battery's cranking amp. capacity will become lower as the battery ages.

Part of the load test also measures the battery output voltage, as the load is applied for a timed interval.

 

from what i can remember from my electronic days, voltage is a minimal indicator of battery health but the only thing we, as laymen, can check. voltage is the window dressing and amperage is the ability to deliver the power. current or amperage is measured by volts/resistance(ohms law). as a battery ages or otherwise becomes less functional, the voltage does not change a lot but the internal resistance goes way up, thus reducing the current before any loads are applied. a load test adds increased resistance to see what kind of amperage is delivered. if the battery is also adding resistance the current delivered will be less than just the applied load resistance thus reducing the current.

whew i'm gonna take a nap

 

When I drive my car long enough to recharge after starting, the reading is usually 13.9 V.
As the battery charges, the charging voltage comes down.
Also, everytime you let a battery go dead, the battery's ability to hold a charge is reduced, and the life is reduced.

 

Actually, a load test applies a decreased resistance across the battery terminals. When the battery isn't connected to anything the resistance is infinite. If you drop your favorite wrench across the terminals the resistance drops close to zero and the battery delivers as much current as it can. Same for starting when you initially turn the key the starter motor isn't turning and its impedance is very low so there is a large current surge until the starter motor gets up to its speed. Typically, starting surge currents run from 400 to 500 amps.

Bill

 

correction noted. i knew i had something wrong! so as a battery ages, its ability to support current caused by less resistance of the load decreases and thus less power. thats why a voltage test without a load will not tell you much but if the battery's own load produces less than 12 v across the terminals then it is an indication of a weakened battery. thanks for the correction, bill.

 

The replacement was from GM and it was made in France...