voltage low on car battery

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Might be a temperature thing. I think the fully charged voltage decreases somewhat at low temperature.
Don Young
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12.6 is considered a fuuly charged battery. See chart
http://www.autobatteries.com/basics/voltage1.asp
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take it to a car repair newsgroup
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On Tue, 03 Feb 2009 21:09:31 -0600, AZ Nomad

I don't know of a good one.
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alt.autos... rec.autos... rec.autos.tech
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On Wed, 04 Feb 2009 07:55:51 -0600, AZ Nomad

Too vague.

I'll try this one next time I have a problem. Thanks.
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Have it tested but 12.3 is maybe 30-40% charged, id say its junk. 12.6 will ruin a battery from sulfation over just 1 year, 12.6 is not a full charge
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battery is probably bad.ocally advance auto parts test batteries for free.
charge for a day, let sit and load test.
lead acid batteries last perhaps 4 years. running a bad batter can lead to damaging alternator. after replacing many alternators i now replace my batteries every 3 to 4 years. alternator failures have dropped to near zero, except getting noisey the bearings wear out.
load test battery if it tests ok forget about it some newer no maintence batteries chargew differently. i have a buddy who uses them for wind power, he has noted differences recently
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Forgetting about voltages for a minute, the key here is that it continues to charge indefinitely at 2 amps. That is not normal and very likely a sign that the battery is on the way out. I take it we still don't know how old the battery is? If it's 5+ years, I wouldn't fool around, just get a new one. Or at keast have it tested.

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snipped-for-privacy@optonline.net wrote:

The key for me, too, was the failure of the charging to taper off. That's why I checked voltage.
The couple own two cars and three pickups besides the van, so they won't be in a jam if the battery fails. So far, it behaves like a good battery: a good sound from the starter, very little drop when the lights are turned on, and no drop in voltage after the battery sits a week. I'm curious.
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Some chargers do not drop off completly If your charger does not have the special circut it will just keep on charging and charging and charging.
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On Wed, 4 Feb 2009 15:18:43 -0500, snipped-for-privacy@webtv.net (Herb and Eneva) wrote:

What is the CHARGING voltage at 2.5 amps after several hours?
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snipped-for-privacy@snyder.on.ca wrote:

I think it was a little under 14. The charger tapers to less than 500ma on most batteries.
It used to be that a charger's regulator was supposed to be higher for maintenance-free than for conventional. I don't know if that has changed.
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On Feb 5, 2:08am, snipped-for-privacy@snyder.on.ca wrote:

There is so much misinformation in this thread (about lead acid storage batteries as used in autos) it's hard to know where to start.
A typical auto battery these days has six cells each, nominally, 2 volts.
Hence such systems are called 12 volts systems. Actually 14 to around 11.8 volts!*
Some boats, heavy trucks and some military vehicles and some aircraft have 24 volt (and occasionally 32 volt) systems. Back in the 1940s six volt systems were common. Although European vehicles, generally, have always been 12 volt. But leave that aside.
But the voltage across each cell, also assuming they are all in good and equal condition and therefore the whole battery, will vary over fairly narrow limits.
Measuring the voltage of standing battery without load is not necessarily a good indication of the state of the battery.
You cannot say something such as; 14 volts = 100%y charged, 13 volts = 75% charged, 12 volts = 50% charged ........... etc. And unlike a propane tank/cylinder you can't weigh the battery to see how much is in it! :-)
Also one bad cell in the series of six can spoil the battery. The bad cell (or cells) either can't pass the electric current through, or is itself sufficiently deteriorated to not output (i.e. turn chemicals back into electrical current). Low temperatures can aggravate the ability of the battery to reproduce the electrcity that has been stored in it.
High temperatures including overcharging** can also cause damage and cause lead sulphation. That's when the battery cells start losing their ability to store electrcity chemically and reconvert it back to electrcity when demanded!
Given that voltage is not an indication of how much capacity the battery has remaining nor does it indicate the capability of the battery to do the heaviest job of all 'Cold Cranking' of a cold engine in winter.
Measuring voltage with of a good or bad battery outside the vehicle is not a good indicator. .
Any battery will most likely show on a voltmeter alone (Which draws a few thousandths of an amp) something over 12 volts immediately after being taken off the charger or immediately after the auto engine engine stops!
However with a reasonably accurate voltmeter it is is possible to measure the battery in operation in the vehicle and get some idea of a) Is it being charged b) Is it capable of providing small amounts of electrcity and also regulate the output of the engine alternator. c) Crank the engine to start it.
a) Maximum voltage should be around 2.3 to 2.4 volts per cell. So 6 x 2.35 = 14.1 volts. So charging voltage should be around 14 volts. b) A reasonably charged battery with engine idling but not actually charge will probably be around 6 x 2.0 to 2.15 volts per cell. So that around 12 to 13 volts. urn on a few lights, with engine idling a good battery should maintain 12 volts. c) Cranking; this is not so much a matter of voltage. Not only will the battery voltage drop as the battery puts out, for very short time, the up to 100 amperes of current needed to operate the starting motor, there will also be voltage drops in the wiring, the starter switch and starter solenoid/relay etc. The voltage might drop to say 8* volts and then recover immediately the internal combustion engine starts and starter disengages.
Here are some practical voltages for lead acid cells used in large installations where the cost is many thousands of dollars per battery string and they must power critical systems, sometimes for 8 up to 24 hours.
A) Recharging: 2.3 to 2.4 volts per cell. (May depend on slight differences and whether North America or European administration).
B) Floating: In service but neither charging of discharging, just waiting with a full reserve, 2.15 to 2.17 volts per cell.
C) Discharging: For very long periods while battery supplies 'all it's got', 2.0 volts per cell.
D) As the last percentage of the battery capacity is used the voltage will then tail off rapidly; how quickly depending on the load at that point. Lights will be dimming etc. voltage will drop to 11.0 volts and below.
The six cell (auto service) equivalents for these are; A) 13.8 to 14.4 volts. B) 12.9 to 13.0 volts. C) 12 volts D) Voltage tails off .............. nothing left.
If battery is charged normally for a normal time period (not overcharged) then allowed to stand for say 10 to 24 hours and then shows around 11.3 volts it is most likely useless!
However a friend who is a mechanic took an old uncharged car battery out of a scapped vehicle to his to his cabin and hooked it up to an old car radio, probably quarter of an amp? And was surprised that it had enough chemical action to run the radio for most of the summer!
As Herb says above, some chargers will automatically time or adjust the charging. Others will just grind away (for a week or more) pushing current into an already fully charged battery. That merely heats up the battery and if severe can cause battery to sulphate; which may/ will reduce it's life and usefulness.
One can charge a dead battery for ever and it will not come back to life. Strengthening the acid, unless some has been spilt is not advisable, it won't make battery any 'stronger'. Water may/will evaporate, especially in heat and depending on type of battery may need to be 'topped up', with chemically pure-clean distilled water.
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terry wrote:

Maintenance-free batteries resist high charging voltages better than conventional ones, and 15V can be appropriate. (I think the appropriate voltage can be higher in cold weather. Modern regulators figure that stuff out.)
In my car, I made a panel meter using a cheap movement, diodes, and resistors. The needle swings 90 degrees between 11.8 and 15 volts. It may serve better than an ammeter. Before I start, when I turn the key I expect about 12.6V. After I start, it shows what the alternator is doing. If it's not over 14 by the time I get home, I know I haven't been driving enough to keep the battery charged and I'd better use a charger. In winter it's often at 15.

I don't understand the chemistry, but it shows me if a battery is charged. Different authorities may give slightly different figures.
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On Thu, 5 Feb 2009 05:00:50 -0800 (PST), terry

You've been pretty well on the mark so far - but you missed it here. A fully charged battery will NEVER sulphate as all the "sulphate" is in the acid. Discharged batteries sulphate.

This is the classic result of "sulphation" All the "sulphate" is in the lead and can't be driven back into the electrolyte. (to turn the water back into acid)

You are right.
Strengthening the acid will make the battery put out more voltage - for a very short time - but will certainly not fix it. It WILL make the Hydrometer read closer to what you want it to read - but that's about all. The plates are still very close to uniform in composition - PbS04 A total waste.
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wrote:

Dang. Do you think, for all the good advice I've given you, they would give me one of the pickups?

I knew a girl, 23, whose blood pressure was routinely 80/40, or maybe 75/30, and she worked fine.
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snipped-for-privacy@invalid.com wrote:

Yup, and unless they say it's only good to use for table salt, I save them and use them on the applicances around here that have starters. Genset, lawn tractor, etc.. They can get quite a bit worse and still run for years on those! Got 5 more years out of the last one on the genset before it started to crank slowly.
Cheers,
Twayne
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On Thu, 05 Feb 2009 04:04:59 -0600, snipped-for-privacy@invalid.com wrote:

MOST of them even have a MidTronics tester!!
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