12.3 volts on a battery indicates it needs to be charged.

IMMEDIATELY after charging a good battery will show a voltage above 13 volts and it will stay there for many many minutes even hours.

If a battery has a shorted cell and is placed on a long charge ending at 2.5 volts per cell.

It WILL show 12.2 to 12.6 volts IMMEDIATELY after charging.

So a battery that is just a little run down and battery with a shorted cell CAN read the same depending on when and how the batteries are checked.

Quoting me and just saying I'm wrong is not helping.

Investigate the term "excess surface charge" as it is used in discussions of lead acid battery charging behaviors.

 

Battery voltage is mostly do do. In any event a battery hydrometer, http://www.amazon.com/K-Tool-International-KTI-70212-Battery-Tester/dp/B0006BIAV4 is a better test. Your really looking for uniformity first and then state of charge. The best angle is use the hygrometer on what you think is a fully charged battery.

Be careful with the battery acid drips. One drip and there's a hole in your pants when you wash them.

 

12.3 volts on a battery indicates it needs to be charged.
IMMEDIATELY after charging a good battery will show a voltage above 13 volts and it will stay there for many many minutes even hours.
If a battery has a shorted cell and is placed on a long charge ending at 2.5 volts per cell.
It WILL show 12.2 to 12.6 volts IMMEDIATELY after charging.
So a battery that is just a little run down and battery with a shorted cell CAN read the same depending on when and how the batteries are checked.
Quoting me and just saying I'm wrong is not helping.
Investigate the term "excess surface charge" as it is used in discussions of lead acid battery charging behaviors.

I think you are contradicting yourself. You said in your first post that 12.3 indicates a shorted cell. Then your first sentence here agrees with my statement that it needs to be charged.
As for excess surface charge, I don't need to read about it. I teach it to my Truck and Coach apprentices all the time, and I know exactly what it is. I have read Battery University forward and backwards and have been an Interstate and Delco battery dealer for years, so I think I am qualified to give the OP the correct information he deserves. A shorted cell cannot be determined by an open circuit voltage test but it would give a good indicator of what is happening. As for hydrometer testing, unfortunately it is going by the wayside and making way for OCV testing because of newer battery design and the fact that most batteries are now maintenance free.

 

Battery voltage is mostly do do. In any event a battery hydrometer, http://www.amazon.com/K-Tool-International-KTI-70212-Battery-Tester/dp/B0006BIAV4 is a better test.

Normally I agree with the hydrometer test. I do remember a problem, where a battery, used to start my Caterpillar 400 kW motor/generator, measured the proper specific gravity all the way down to 7-8 volts. Theory wasn't working that day ... and for a damm good reason.

Of course this had me wondering WTFO. Turned out, someone told the young non-rate to add acid when the hydrometer wasn't reading the correct specific gravity.

 

Theory would have worked if you had all of the variables. Interesting though.

 

Belt or belts slipping/Excessive voltage drop on positive or negative side of circuit

Voltage regulators in vehicles are set between 13.6 - 14.4 VDC. A voltage regulator does not drop in voltage when RPM is increased.

Really?????????

No, does not matter. You have another problem. Your battery is sulphated. Causes can range from buying batteries that were on the shelf for a long time to the fact that it sits for a few days and then you make short trips and never get it fully charged again causing your voltage to drop each time. You could also have a parasitic draw that is pulling your battery down constantly and slowly. This would probably be the most likely cause.

Batteries in a low state of charge can be that way for a number of reasons. One of the biggest is sulphation. A car battery has an average life span of 5 years and that includes the time it sits on the shelf at the parts department before you buy it. Modern day handheld testers are not valid in many ways and if they are not tested by carbon pile, there is no way of knowing for sure if they can handle the cranking motor load. Sulphated batteries cannot be resurrected or brought back to life successfully despite all the hoopla on the Internet saying they can. Sulphation is a crystalline structure that when broken away from the plate by "blast" charging, takes part of the sponge lead or lead peroxide with it, reducing the plate surface area. The original battery in this story, was more than likely sulphated and at the end of it's life. As for battery charging, standard lead acid batteries must not be charged over 15.5 VDC or they will start to boil. AGM and GEL batteries are in the area of a maximum of 13.8-14.1 VDC respectively. Higher than that and they will sizzle. They are much better at deep cycling that SLA batteries.
Charging system voltages can be reduced at higher RPM by a number of factors as I mentioned, but often times when an alternator has been subject to a bad battery, it will either fail or it will fail soon after the battery has been replaced. It has burnt itself out trying to charge a dead battery and has worked really hard to do that. As you all know, diodes do not like heat. Poof.
Glad to hear you have your glow plug issue sorted out. You could do that yourself with an inductive ammeter test. Simply check each glow plug current draw when the key is cycled. They should all be the same. Best to replace as a set. The others will follow shortly.
Cheers!

Hi,

Interesting info, thanks.

I find that if i charge the battery at a higher than in-the-car voltage from the alternator i can lower the impedance of the battery once the voltage gets lower. Let me explain in more detail.

Over time, the voltage gets lower and lower but also the impedance gets higher and higher, and that means that once the car is started the somewhat low voltage (14v) of the alternator is not enough to charge the battery quickly. That's because the higher impedance acts like a series resistor, limiting the current that can get to the battery from the somewhat constant voltage from the alternator. Limiting the current like that means it takes a lot longer to fully charge the battery, so for a short trip it does not charge enough.

Putting the battery on a higher voltage charge gets around the higher impedance problem. so the battery charges enough, and the impedance drops back down again. NOW when put back in the car, the alternator somewhat lower votlage is enough to charge the battery in a faster time, so short trips charge the battery, almost. It still falls short if there are always a number of short trips, and that's my most likely driving pattern.

So i dont know what the formal name what is happening to the battery is, but that's the description of what happens.

 

Your battery is sulphated. When you make short trips, your battery does not get a full charge. Your starter takes a lot of power from the battery to crank it over. It takes 10-20 minutes of driving time to replenish that loss. When the vehicle sits, it is losing charge as well. A chemical reaction now starts to take place and sulphate attaches to the plates and forms a crystalline wall and slows any electron movement. This is your high impedance. Now it takes more pressure to push the same amount of electrons through the battery. Look up three minute charge test and you will see what I mean.
When a battery becomes sulphated, the best way to remove the sulphate, is to slow charge the battery. I believe this is what you are doing when you remove the battery and charge it in the house. By doing this, you sort of restore the battery back to a higher level but remember that each time you have to do it, it is not as strong as the time before. Eventually, this will no longer work as the battery ages.

 

Here's my understanding of lead acid car batteries: They are nominal 12 volts. They will typically read 12.2 to 12.6 volts when fully charged. DURING charging (such as after you first start the car) the voltage should pop up into the 14 volt range, typically 14.2 to 14.4. 14.6 is not uncommon but is somewhat indicative of a problem with the battery. After a minute or two the battery voltage should drop down to 13.6 volts - that's their float charge voltage. When the vehicle is operating the battery voltage should not go below 13.6 volts. If it does then that may indicate either a bad alternator OR a slipping belt.

When checking the health of a car battery, I start by checking its voltage BEFORE starting it. If it's a new battery I expect it should hold that voltage even with the lights, AC and fan on. It shouldn't drop below 12 volts. If it drops into 11.8 (per sé) it may be a little on the older side. But it should still be strong enough to do its job.

If it falls to 11 volts then the battery is probably old and in need of replacement. During startup there is a heavy current draw. It's not uncommon to see a battery drop into the 10 volt range during startup. Even that momentary spike of current, the battery shouldn't drop below 10 volts. But because it's so short it's difficult to get an accurate reading - so I normally don't worry about voltage during startup. I just don't have a scope with a memory to capture that dip in voltage.

Before you accuse your battery of being old and in need of replacement, evaluate the charging system. Like was mentioned earlier, 14.4 is normal. 15 volts suggests a weak battery. High internal resistance can be to blame for the high reading. But make sure you don't have a slipping fan belt. If the battery is not being properly charged then its not the batterie's fault. If the fan belt isn't slipping then verify the output of your alternator by looking for 13.6 volts during operation. Turn on all electrical devices possible. Voltage should STILL not drop below 13.6 volts. If it does then your alternator is suspicious. Could be a bad coil or diode - or regulator.

Know before you spend. Or spend and learn what wasn't the problem.

 

I just noticed this post is about 2 1/2 months old. You've already probably solved the problem.

 

I just noticed this post is about 2 1/2 months old. You've already probably solved the problem.

Problem was solved. Battery and glowplugs were replaced.

 

Tonyr1084, I want to clarify a few things for you. I think some of your points are a little misunderstood but you are on the right track.
Batteries when fully charged, in or out of the vehicle, are 12.6 volts (2.1v/cell). A battery that is 12.4 volts is only 75% charged. 12.4 is minimal I would ever want to see for a battery. Below 12.4 volts, it is at the beginning of discharge and sulphation is starting to take place.
In regards to the charging system, typical voltages could be anywhere between 13.5 and 14.5 volts but the best range for it to be in is in the area of 14.0-14.4 VDC. This is set by the voltage regulator and is sensed from the battery either by the main wire or a separate sense wire. When operating , the voltage regulator attempts to maintain this setting by switching the regulator on and off very rapidly (PWM) and controlling the rotor voltage (field) to keep the battery fully charged. When starting the vehicle, the battery voltage will drop down due to the high current draw of the starter, and then you should see a large current draw (alternator turning on and attempting to replenish the battery quickly), followed by a leveling out of the current as the battery charges. If the charge current stays high, it means that there are large consumers online asking for excessive current, or the battery itself is sulphated and is requiring more of the alternator to charge.
When all devices in the vehicle are turned on, the system is designed to maintain charge voltage but the minimum you want to see is 12.6VDC. If it falls below this point, there is a problem. It could be in the alternator or it could be voltage drops in the wiring. Without proper testing, it is hard to tell. The main point here is that it should not drop below 12.6 VDC.
If your battery voltage climbs above 15.0 VDC when charging, the battery is not to blame. It can be in the voltage regulator or in the sense wire I mentioned earlier. Remember, the voltage regulator uses a zener diode to dump excess voltage so it should never climb beyond that sense point.
In order to properly assess a battery, the following should be done:
1) Visually inspect battery for any signs of damage, cracked case, corrosion etc. Clean and verify condition.
2) Make sure the battery is fully charged and the surface charge has been removed. The battery should be at 12.6 VDC if done properly
3) Assess state of charge using a hydrometer or refractometer (old school) or check the Open circuit voltage (new school). A minimum of 12.4 VDC is necessary to perform a load test
4) Perform a load test using an AVR or carbon pile at 1/2 CCA for 15 seconds. This tests the integrity of all the plates and simulates the cranking motor. The battery should be above 9.6VDC at 70 degrees. Below that is a fail.
5) To check for sulphation, a 3 minute charge test or EIS test (impedance) can be performed using a handheld unit. This is also the test of choice over AVR testing now because there is limited brain work involved. Not my first choice but the industry likes it so...

Anyways, this testing should all be done by a trained professional and this is basically the only proper way a battery can be assessed. I should mention the EIS tester can also test batteries even when they are already in failure mode.

 

Well, B Williams, age 56, You've done it. I never would have believed I could ever find someone smarter than me. But now I know better.

OK, so 12.6 is nominal voltage. 12.4 is 75% discharged. MMMmmm, lets see if the math agrees:

12.6 x 0.75 (75%) = 9.45 volts. HEY! HOW DID YOU DO THAT? HOW DID YOU MAKE 75% OF 12.6 EQUAL 12.4 VOLTS? You need to explain yourself.

You've made some obvious comments that are beyond my knowledge. Back in the day when I was servicing emergency lighting systems (12 volt lead acid systems) a 12 volt battery was "NOMINALLY" 12 volts. All calculations were based off of that nominal voltage. And when a battery was at 80% discharge (not 75%, 80) it was considered dead. It had no useable energy left. So according to what I said (and the math to support it) equals 9.6 volts. Do the math. And not the Republican math.

You said that alternators use zener's to dump excess voltage. Honestly, that's a subject I DO NOT know about. I don't challenge you on that. But I have, in my many years of automotive diagnostics, seen shot batteries have the alternator pump out as much as 14.8 volts, which to me has always been a sign of a battery that is not up to snuff (whatever you consider snuff to be). Maybe they DO use zener's to dump excess voltage. And WAY back in the day, they had regulators that were a series of power resistors and relays that controlled the current to the field winding of the alternator. So it's always been my understanding that alternators governed their output by controlling the field winding current. More current more magnetic saturation. More saturation, more transfer to the three phase coils of the stator, more voltage generated to support the automotive electrical system AND to recharge the battery.

With batteries comes internal resistance. In a "PERFECT" battery there is no resistance. But in reality, there is no such thing as resistance. And as resistance goes up current goes down. Now, I'm NOT the expert on batteries either. However, I'm glad to share what I know - or have been lead to know - or believe. If I'm wrong then so be it. I'd be glad to hear "Hey Tony: They've changed things. They no longer behave - - - ". Whatever you may know, you're free to share. Right or wrong, your opinion is valid - and valued. As I would hope mine would be. HOW you say what you say is just as important as WHAT you say. I don't need people speaking condescendingly toward me. I've disagreed with others here before and some of them have taken offense and others have appreciated my input. I'm NOT the expert here. One thing I don't like to do is open my mouth and be wrong. But sometimes I am. Am I wrong about this battery post? I don't think so.

So if you can prove your points with facts (such as math) then please do so. A single cell MAY BE 2.1 volts. It's been a VERY LONG TIME since I've done much with Lead Acid batteries, and perhaps you're right. I DO know that many times (on older batteries) I've checked their voltages at rest (when they've sat overnight doing nothing) and found them to range from 12.2 to 12.6 volts. Those batteries have performed quite well (as you would have called a 12.2 volt battery dead). I've found batteries (in my history) to be at 11.8 volts - and those were batteries that were giving me trouble, BUT still did the job they were asked to do. Batteries that were much below that (say 11.6 volts) were problematic or worse, and those were the batteries that were candidate for change.

But to blame a low voltage on a bad battery is a mistake. First one needs to verify the charging system. I've seen (historically) battery voltages go up to 14.4 volts (highest I've ever seen with an electronic regulator), and watched them drop to 13.6 volts after a few minutes. On a good charging system I've NEVER seen it go below 13.6 volts with the engine running. NEVER. Not just after a few minutes, I'm talking about battery/alternator charges after hours of driving. 13.6 volts.

In fact, car radios are not designed to work on 12 volts, though they do - they're designed to work on 13.6 volts. So the alternator is expected to support the auto electrics AND replenish the battery. A battery held at 13.6 volts suffers no bad side-effects. But a battery held higher (say 14 volts or more) causes the cells to evaporate. Whether charging current is controlled by PWM or some older method, the target voltages are still the same. I'm unaware of any real changes to Lead Acid batteries that would make any significant differences to the way charging systems are expected to perform. But to think that during operation a car battery and alternator voltage should be at 12.6 volts - well, that's just too hard for me to swallow. I'll say it again, I could be wrong - I'm not the consumit genius on these subjects, but I DO believe what I said was correct.

Now, if the OP wishes to follow your advice - that's fine too. Free world, You know, that stuff about free speech. But please don't take such a condescending attitude with others when you disagree with them. I try not to. But sometimes people just pizz me off. Thanks for starting my sunny day off just a little more cloudy and yellow.

 

Did some research. Found nothing to change my mind on the things I've said, but I DID learn a thing or two. Follow this link (below). It starts at page 1. Clicking the NEXT PAGE (topic in blue) does not always take you to the next page. Simply click on page #2 when ready to go to page 2. Page 3 and so on. You'll learn something about batteries and the proper maintenance techniques along with several myths about batteries. Watch carefully and you'll see some of the things I've already stated. I found nothing to contradict anything I've said so far. I was hoping for a little more support, but nonetheless, I think this link will help clarify any misinformation ANYONE here might give you.

http://autorepair.about.com/library/weekly/aa101604a.htm

I mentioned learning something. I remember my father telling me that putting a car battery on concrete will discharge it. I believed that ALL THESE YEARS. Turns out it was just a myth (in my day - but not in my father's day). There's ALWAYS things to be learned.

I respect the opinions of others, even when they conflict with my opinion(s). It's what makes the world go round. AND we learn things from others. Keep an open mind and never think your opinion is the most superior one out there. Remember, opinions are like azz holes. Everybody has one. And some may stink. That applies to my opinions too.

 

OK, so 12.6 is nominal voltage. 12.4 is 75% discharged. MMMmmm, lets see if the math agrees:

12.6 x 0.75 (75%) = 9.45 volts. HEY! HOW DID YOU DO THAT? HOW DID YOU MAKE 75% OF 12.6 EQUAL 12.4 VOLTS? You need to explain yourself.

It doesn't work that way - voltage and state of charge (SOC) are not linearly related and certainly the intercept where SOC goes to zero is not 0V. A battery showing 9.45 volts open circuit is beyond discharged and may be ready for the recycler.

Unfortunately, the relationship of voltage to state of charge (SOC), while well known, is complicated by the temperature and the current load when the voltage is measured. So it is never accurate to talk about voltage and SOC without also specifying those other critical factors.

That all said, a battery under light load (C/100) and ambient temperature (65°F ?) is considered fully discharged at 11.7V and fully charged at 12.7V. Proper battery tending keeps the battery in that 1V range for its entire life. A slight excess while charging, say 13.5V, is required to drive any significant current in and overcome the internal resistance.

I can loosely support bwilliams statement that 12.4V on an unloaded battery indicates ~75% discharge.
If you see 12.4V at C/10, then you're up around 80% of full charge.

 

 

Guess its time I learned something. Sorry for having sore feelings.

 

The hardest things to learn are the things we think we already know.

 

Interesting fyi, just bought a 2008 Buick Allure and was heading out on the highway one day and noticed the voltmeter showed 11.9 volts. Checked in the manual and it states normal operating voltage varies between 11.5 and 15.5 volts. Seems the alternator is controlled by the ecm or bcm on newer cars. Something to remember when troubleshooting.

 

@bwilliams60:

I come here humbled by my learning experience. I wish to thank you for pointing out things I did not know. Fact: We all know what we know, but we never know what we don't know. After doing more research on batteries I've changed my point of view on what constitutes a good battery.

Turns out the proof was sitting in my garage. I bought a battery for my wife's car this past January. I took it out because the car has suffered a major mechanical malfunction. After a few days of sitting on the shelf I tested the battery voltage. Boy was I surprised to see it sitting at 12.69 volts. Of course this was totally isolated from any parasitic drain. I always considered a 12 volt battery to be nominally 12 volts with just a few tenths above showing a good "State of Charge". I was wrong at that. I also learned that a battery can be fully at 12 volts (respectively) and have absolutely no charge to it. Another case in point: I remembered many years ago a college professor had an 80 volt battery he was throwing away. I asked why he was and he said it was dead. I asked if I could have it and he had no problem with that. I took it home and measured its voltage. It was 80 volts. HOW could that be a DEAD battery? Well, I couldn't do anything with it. I eventually stuck a red LED across the leads expecting it to pop. It didn't. It lit up as normal as any red LED of that day. So I employed the battery and Led as a way of checking christmas lights. The kind where when one goes out they all go out - if the LED lit up then the bulb was good.

Suffice is to say - My apologies and thank you for helping me learn something new.

 

Tonyr1084. I want to thank you for your tag. I have been a little beside myself over this as I started to question my teaching abilities and my ways of teaching. I didn't mean to be condescending in any way and my statements come from literally 1000's of tested batteries in the field.If I give out false information, I hope someone calls me on it but līke I said, I don't usually post unless my facts are correct. I hope we can move forward and put this behind us and all is good.
Have a nice day and we will see you somewhere around here.