Battery experts, I need your input

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The_Eric

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As part of my periodic checking, I threw the multimeter on my car battery. It checked 12.3ish volts in 20 degree weather. After a 30 mile round trip drive, it was up over 13 volts. Figuring this was the surface charge, I turned on the headlights and monitored the voltage. It dropped like a rock until 11.8ish volts and stayed there. I've got the charger on it now and aim to leave it on overnight, but I'd like to know know your thoughts.

Extra info:

-Meter is a Fluke model 78 (sold under the Matco name)
-Battery is a few months old- I installed it early in the summer
-Charging system is up to snuff and voltage is 14.6v on a chilly day after start up. It does come down with temp to the high 13's to low 14's
-Battery was charged prior to installation and again a few months later due to low voltage (12.3ish)

At this point, I'm thinking it's just a bad battery, but I've also tested it with one of those $70.00 electronic testers randomly and it's always passed with flying colors.

Another question: My charger seems to like to charge at 13.3 volts on the low setting and 17+ volts on medium. I don't know exactly how much over 17 it goes, I don't know as I chickened out. I've used it for several years, frequently using the "Medium" setting without issue, but this was the first time I've actually thrown a meter on it. It's supposed to be 2 amps on low, 10 amps on medium and 40 amps on high. Is this normal? Maybe it was this high due to the relative high voltage of the battery?

FWIW, the charger is close to 10 years old and is labeled as a Matco unit. I don't know who actually made it though.
 
Last edited:
Not an expert but I don't think you need to charge it. You may end up overcharging it and wreck it.
 
I have read that those battery testers are pretty much useless.

What kind/brand/size battery is it?
What year/type of vehicle?

The colder the temp the higher the voltage needs to be to squeeze the amps into the battery and fully charge it.

You also need to check the alternator voltages at rpm's higher than Idle speed. If the battery is not fully charged it makes a big difference in what voltage you will see at idle as opposed to higher rpm's

Also a fully charged battery might be recognized as such by the vehicle, and the voltage might read only 13.6. The vehicle drops the voltage so it does not overcharge the battery and cause excessive water consumption.

I don't have a temperature compensation chart handy, but 17 volts is much too high for the charger unless both battery and charger are in sub arctic conditions.

Get yourself a hydrometer, unless you have an AGM battery. While most hydrometers are not very accurate, they are good at comparing cells within the same battery.

Headlights can consume 15 to 25 amps. With a small, cold battery, I do not think 11.8 is too bad. Does the voltage rebound after turning the lights off?

If you suspect the vehicles charging system might not be working to 100%, clean the engine and alternator grounds, and make the battery terminals look like silver. Any white or green corrosion on the battery terminals can indicate the wire within is highly resistant when faced with higher amps.

Also, do you regularly use the battery to listen to music or consume battery power in other ways with the engine off? Starting batteries are really only designed to be drained 5%, and recharged quickly. If drained further, they do not hold up well, and a dual purpose/ marine type battery would give better service but will need to be slightly larger to provide the same CCA ratings as a starting battery.
 
What caused you to do all this "checking"?

Assuming an accurate meter, a fully charged battery will stabilize at about 12.7 volts..... several hours after charge/discharge events are completed.

If the battery had 11.7 volts - no load - then it would be nearly dead.

A non-sealed battery, lead-antimony construction acts like a zener diode when fully charged, bleeding off excess charge by electrolysis - bubbling off the water and converting it to hydrogen and oxygen... and causing a need to refill the battery.

A lead-calcium battery, when attached to an unregulated charger like yours simply stops accepting a charge when full, causing the open circuit voltage to rise much higher. My unregulated 2 amp charger will push a sealed battery well past 15 volts. That means its full of course, stop charging it!!

IS there anything this battery is failing to do for you?? It may be totally normal!
 
Doesnt sound right. Battery likely has internal short and some damage. Get your alternator checked off car before replacing the battery.
 
What am I missing? I have read the original posting several times.

The car starts ok?
The headlights light ok?

Is all this worrying just over the slight variation in expected voltage readings?
 
Originally Posted By: Warstud
Not an expert but I don't think you need to charge it. You may end up overcharging it and wreck it.


+1

The voltages you quote are normal. They are not showing any problem. If you do over-charge it you can damage it.
 
Originally Posted By: wrcsixeight
I have read that those battery testers are pretty much useless.

What kind/brand/size battery is it?
What year/type of vehicle?
Specs are 2001 Hyundai Elantra with a group 124 battery. It is a an O'Reilley's branded East Penn made unit rated at 670cca and 800ish ca
The colder the temp the higher the voltage needs to be to squeeze the amps into the battery and fully charge it.

You also need to check the alternator voltages at rpm's higher than Idle speed. If the battery is not fully charged it makes a big difference in what voltage you will see at idle as opposed to higher rpm's

Also a fully charged battery might be recognized as such by the vehicle, and the voltage might read only 13.6. The vehicle drops the voltage so it does not overcharge the battery and cause excessive water consumption.
This I'm aware of.
I don't have a temperature compensation chart handy, but 17 volts is much too high for the charger unless both battery and charger are in sub arctic conditions.

Get yourself a hydrometer, unless you have an AGM battery. While most hydrometers are not very accurate, they are good at comparing cells within the same battery.
No can do. The battery, while still a flooded cell battery, is sealed- no access.
Headlights can consume 15 to 25 amps. With a small, cold battery, I do not think 11.8 is too bad. Does the voltage rebound after turning the lights off?
Yes, it does.
If you suspect the vehicles charging system might not be working to 100%, clean the engine and alternator grounds, and make the battery terminals look like silver. Any white or green corrosion on the battery terminals can indicate the wire within is highly resistant when faced with higher amps.
At this point, connections are not suspect. They all appear to be clean and free of corrosion.
Also, do you regularly use the battery to listen to music or consume battery power in other ways with the engine off? Starting batteries are really only designed to be drained 5%, and recharged quickly. If drained further, they do not hold up well, and a dual purpose/ marine type battery would give better service but will need to be slightly larger to provide the same CCA ratings as a starting battery.
No, I do not.




Originally Posted By: fsskier
What caused you to do all this "checking"?

Assuming an accurate meter, a fully charged battery will stabilize at about 12.7 volts..... several hours after charge/discharge events are completed.

If the battery had 11.7 volts - no load - then it would be nearly dead.

A non-sealed battery, lead-antimony construction acts like a zener diode when fully charged, bleeding off excess charge by electrolysis - bubbling off the water and converting it to hydrogen and oxygen... and causing a need to refill the battery.

A lead-calcium battery, when attached to an unregulated charger like yours simply stops accepting a charge when full, causing the open circuit voltage to rise much higher. My unregulated 2 amp charger will push a sealed battery well past 15 volts. That means its full of course, stop charging it!!

IS there anything this battery is failing to do for you?? It may be totally normal!


No, it starts the car just fine, however on occasion it doesn't seem to spin the engine over with quite the authority it usually does.


Originally Posted By: fsskier
What am I missing? I have read the original posting several times.

The car starts ok?
The headlights light ok?

Is all this worrying just over the slight variation in expected voltage readings?


The worry stems from the 12.3 volts (after a day's rest) and the fact that 12.3 volts is listed as 50% charged. I also thought that a discharged battery can suffer from sulfation. Also cause for concern was the fact that the headlights dropped the voltage very fast to 11.8

I guess all in all, it's just me being overly cautious and wanting my battery to give me many years of trouble free performance.
 
Measure the battery voltage with the engine runnning.It should be more than 14vdc-a lesser voltage would indicate charging system trouble
 
17 volts charging is way to high. Should not get much over 15 volts.

Are you sure you don't have a draw on the system. On car charging sounds about right. Sounds like the voltage is dropping fairly fast. Have you tried checking the voltage after 8 hours. That is about the time the voltage should have settled down. But if you have a draw on the battery somewhere that whole idea is out the window.
 
Don't forget temp. What is the battery or outside temp when you're measuring your voltage?

A battery can be 100% charged at 12.8v at 70F room temperature and the same battery will only read 12.3v at 32F and 12v at 0F. Regardless, it is fully charged and it'll still start your car. So, the colder it gets, and the older the battery gets, its going to turn over a little slower.

Sounds to me that your battery is perfect. If the car starts after sitting a couple days, quit playing mechanic and find something else to worry about.

How old is the battery? warranty?

If any battery is >5 years old, and you have a fear of missing an appointment, a job interview, have an expecting wife, an on call career, or can't miss last call at the pub, just replace it already.
 
Even if the battery is bad, you will have to prove it to the store where you bought it from. Take it to them and let them check it.

- Vikas
 
As long as we're on the subject, how do I know when to use the 2 amp setting versus the 10 amp or 55 amp setting on my charger?

I always use the charger at 2 amps and let it charge for 48 hours. This is mainly for cars that are in storage and the batteries won't start the car. It's been working fine so far over the years.
 
Last night I left the dome light on in my truck. Probably the 3rd or 4th time I have done this. It started fine this morning although it was in a garage at about 55F. I drove home about 25 miles. Today I have it on my BMW motorcycle charger that goes into float mode at about 13.8 volts. It has been charging for several hours now at about 1 amp and has not kicked out. Seems like it took a hit from a slow drain all night. Usually it will go into float mode after after 15 or 20 minutes. Time will tell. I have always found slow and low is better to rejuvanate lead acid batteries. Hope I have not shortened the life of my battery.
 
Originally Posted By: Hermann
Last night I left the dome light on in my truck. Probably the 3rd or 4th time I have done this. It started fine this morning although it was in a garage at about 55F. I drove home about 25 miles. Today I have it on my BMW motorcycle charger that goes into float mode at about 13.8 volts. It has been charging for several hours now at about 1 amp and has not kicked out. Seems like it took a hit from a slow drain all night. Usually it will go into float mode after after 15 or 20 minutes. Time will tell. I have always found slow and low is better to rejuvanate lead acid batteries. Hope I have not shortened the life of my battery.


I agree slow and low. Unless the battery has been flattened out. Then you need to ram it with some amps to get it started charging.
 
Low and slow 'might' be better for a battery that is nearly fully charged, but for one that has been drained below 80%, low and slow can mean never fully charged, depending on the low and slow source.

Leaving the Dome light on for 12 hours can consume 8 to 24 amp hours from the battery. Most car batteries are around the 74 amp hour mark.

Starting batteries should never be drained below 80% charged.

Dual purpose/rv/marine/trolling batteries should never really be drained below 50%

True deep Cycle batteries should never be brought below 20%.

The less any battery is discharged, and the quicker it is brought back to full charge, the longer it will last. Deep Cycle batteries are just more tolerant of deeper discharges. Starting batteries can be destroyed in as little as 12 cycles to 20%. A true deep cycle battery might be able to be cycled 500 times to 20%.

On a charger with a 2, 10, and 40 amp setting, I would use the 10 amp setting on a regular sized car battery. As it gets nearer to full charge, the amps it can accept drop down to the 2 amp level anyway.

The 40 amp feature might just be a boost feature for helping to start a vehicle whose battery was drained dead. Only a few chargers are rated to constantly output 40 amps
 
I figured that since it started right up and I drove home for over a half hour that it got its hard charge during the drive home. Used the slow and low to finish the job. When I finished charging the little green Delco eye was bright green.
 
Originally Posted By: wrcsixeight

Leaving the Dome light on for 12 hours can consume 8 to 24 amp hours from the battery.


Probably on the lower side of that--my Crown Vic's ticket light has a 24 watt bulb in it, and it's way brighter than any normal dome light.
 
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