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Old 04-27-2016, 08:23 AM
 
483 posts, read 353,010 times
Reputation: 120

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Quote:
Originally Posted by eddie1278 View Post
It's not 12 volts it's 12.6 because each cell is 2.1 volts.

If the battery is

12.5 = 85% charged
12.4 = 65%
12.3 = 50%
12.2 = 35%
12.1 = drained

Is this true? I read conflicting answers all over the internet.

Reason I ask is I just bought a battery from Advance Auto parts about a month ago and noticed it has been slightly slower cranking over the first start of the day. So I checked it with my meter and it reads 12.4 - 12.5

The truck starts right up no problem after I ran the truck and shut it off during the day. So to me it sounds like the battery is not holding a charge overnight.

I went back to autozone and they used a machine that puts a load on the system and prints out a receipt that says it's good. The battery is rated at 775 CCAs but on the test came out 830 CCAs and 12.9volts.

The idiot who did the test told me "well the battery is at 12.9 volts" I said that's because I drove the truck here and the alternator charged it up its a surface charge. He says something nooo

Anyway these guys know just enough to be dangerous.

Those machines don't tell the voltage or how charged the battery is. Sure the machine will say good if it has enough power to do the load test even if it's drained some.

So is it true I should have a 12.6V reading on a fully charged battery anything less it needs to be charged? And it shouldn't dip under 12.6 in less then 24 hours?
more beginner questions if you don't mind. WHen it's at 12.1 or lower where it's drained, can you still charge it back up to 100% heatthy state? or battery is gone?

when you start up the car and the voltage is under 13.8..that means alternator is bad? and during start up when voltage drop below 10v does that mean battery is going? EXACTLY what voltages should you be buying up a new battery?
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Old 07-20-2016, 12:37 AM
 
483 posts, read 353,010 times
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I check my battery voltage and it's 12.84...why so high? I turned to accessories and turn on headlight for 3 minutes then checked it.

battery is 2.5 years old, 13.5k miles.
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Old 07-22-2016, 07:59 PM
 
1,964 posts, read 2,381,785 times
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Quote:
Originally Posted by LVguy View Post
more beginner questions if you don't mind. WHen it's at 12.1 or lower where it's drained, can you still charge it back up to 100% heatthy state? or battery is gone?
You may want to review some of the other posts in the thread. The voltage readout alone is insufficient to determine whether the battery is still good. You may have good voltage but not generate enough current under load. You will also need to perform a load test. Remove the battery from the vehicle and take it to an auto parts store that will perform this test for you.
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Old 07-22-2016, 08:22 PM
 
2,746 posts, read 3,421,309 times
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Quote:
Originally Posted by LVguy View Post
I check my battery voltage and it's 12.84...why so high? I turned to accessories and turn on headlight for 3 minutes then checked it.

battery is 2.5 years old, 13.5k miles.
That's just a "surface" charge. It will read high after you drove the vehicle or started it. Check the voltage in the morning it will be lower no higher then 12.6 for sure.
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Old 10-25-2016, 07:48 PM
 
2 posts, read 8,706 times
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The voltage meter in my 04 toyota says 16-17 on a 0-18 gauge... The needle staying there and doesn't change....is this high and a problem..
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Old 10-25-2016, 07:49 PM
 
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So what should I do I in the am it is still at 16-17
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Old 10-25-2016, 08:02 PM
 
2,746 posts, read 3,421,309 times
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Quote:
Originally Posted by Southern Shon View Post
The voltage meter in my 04 toyota says 16-17 on a 0-18 gauge... The needle staying there and doesn't change....is this high and a problem..
yes something is wrong there a running vehicle should have a voltage between 13-14 volts. Take it to advanceauto parts or autozone they do free battery and alternator checks.
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Old 10-26-2016, 12:09 AM
 
Location: Denver
3,138 posts, read 6,901,436 times
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Quote:
Originally Posted by eksine View Post
State of Charge

Here are no-load typical voltages vs state of charge

(figured at 10.5 volts = fully discharged, and 77 degrees F). Voltages are for a 12 volt battery system. For 24 volt systems multiply by 2, for 48 volt system, multiply by 4. VPC is the volts per individual cell - if you measure more than a .2 volt difference between each cell, you need to equalize, or your batteries are going bad, or they may be sulfated. These voltages are for batteries that have been at rest for 3 hours or more. Batteries that are being charged will be higher - the voltages while under charge will not tell you anything, you have to let the battery sit for a while. For longest life, batteries should stay in the green zone. Occasional dips into the yellow are not harmful, but continual discharges to those levels will shorten battery life considerably. It is important to realize that voltage measurements are only approximate. The best determination is to measure the specific gravity, but in many batteries this is difficult or impossible. Note the large voltage drop in the last 10%.

State of Charge 12 Volt battery Volts per Cell
100% 12.7 2.12
90% 12.5 2.08
80% 12.42 2.07
70% 12.32 2.05
60% 12.20 2.03
50% 12.06 2.01
40% 11.9 1.98
30% 11.75 1.96
20% 11.58 1.93
10% 11.31 1.89
0 10.5 1.75
Back to top

Why 10.5 Volts?

Throughout this FAQ, we have stated that a battery is considered dead at 10.5 volts. The answer is related to the internal chemistry of batteries - at around 10.5 volts, the specific gravity of the acid in the battery gets so low that there is very little left that can do. In a dead battery, the specific gravity can fall below 1.1. Some actual testing was done recently on a battery by one of our solar forum posters, and these are his results:

I just tested a 225 ahr deep cycle battery that is in good working order..
I put a load on it 30a for 4 hrs it dropped its voltage to 11.2
I then let it cool down for 2 hrs

then put the load back on again in 1hr 42 mins it dropped to 10.3v
35 mins under 30a load 9.1v (273w)
10 mins later max output current 11.6a 8.5v (98.6w)
5 mins later max output current 5.2 amps 7.9v (41w)
3 mins later 7.6v and 2.3a (17.5w)

This shows after it gets below 10.3 v you only have 35 mins of anything useful available from the battery.

battery is now dead and most likely will not fully recover
I find it interesting that in 4 hours you took 120 amps from the battery it pretty much killed it.
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Old 10-26-2016, 12:11 AM
 
Location: Texas
5,586 posts, read 11,831,318 times
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It will depend on the vehicle as to what you'll get. Ford will usually charge more than other makes. My F150 with a 150 amp alternator will charge at max voltage of 14.2 volts. The battery after sitting over night will read 13.7-13.8 volts. My brothers Tacoma charges at 13.8 volts and at rest after 8 hours will be at 13.1-13.2 volts even on the same battery from my truck. My sisters Jeep Laredo charges at 13.2 and the battery at rest will be 12.8 prox. None are over charged and none are under charged. My battery has never needed any water and neither has bros or sister. My previous F150 was the same as far as voltage and over 100,000 miles never needed any battery service at 14.2 volts. My Bronco runs the same voltages and the battery in it is now 9 years old and starts the truck just fine. Bro on the other hand can't seem to make a battery last over 2 years regardless of brand or cost. Sister doesn't seem to have battery issues at all.
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Old 10-10-2017, 04:59 AM
 
6 posts, read 16,787 times
Reputation: 11
its copied from the NORTHERN ARIZONA WIND & SUN, it's not my work. I used this info when researching solar panels and batteries for off-grid: https://www.solar-electric.com/learn...ttery-faq.html

Quote:
Originally Posted by wankel7 View Post
I find it interesting that in 4 hours you took 120 amps from the battery it pretty much killed it.
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