battery voltage

Bill from MA · Mar 5, 2009

After the help about my battery problems ( http://www.ytmag.com/cgi-bin/viewit.cgi?bd=ttalk&th=691577 ) I pulled the batteries and have them in my cellar to try to get things going again this spring. I put them both on a slow charger for about 4 hours. If you put a tester on a 12 volt battery what should the voltage be when fully charged?

One is at 13.9 and the other 13.2. Is 13.9 fully charged?

Thanks,
Bill

John T · Mar 5, 2009

A 12 volt battery consists of 6 cells each of approximately 2.1 volts so a good battery just sitting there not attached to any charger etc should read right around 12.6 volts fully charged.

Then when hooked to a good working charger such as a generator or alternator etc. it should rise to at least 13 to around 14.5 and a bit more DEPENDING on if its a genny or alternator and its voltage regulator etc and the battery condition

Many auto stores can perform a battery load test an hydrometer test at no charge

John T

buickanddeere · Mar 5, 2009

12.6V is the normal charged voltage. The high reading are due to capacitive effect from recently being on the charger.
Putting the battery in a machine, turning on a small 5-10 amp load such as lights.Then measuring the voltage after a minute is a reasonably true test of "resting voltage".

ken in texas · Mar 5, 2009

Four hours on a weak battery is not enough time.I would reccomend at least 24 hours,slow chargeing,while keeping a close watch on them,making sure they don,t boil.be sure you ventilate the area to prevent a build up of explosive fumes.A cellar may be a dangerous place to charge batteries

Allan in NE · Mar 5, 2009

Hi Bill,

Ya can't measure 'state of charge' with a volt meter, as battery voltage remains "relatively" constant, charged or not.

Allan

Anonymous-0 · Mar 5, 2009

I have seen 14.2 on my Ford powerstroke when its running, I had a problem with the altenator so I was checking for charge out put. Most batteries unhooked I have show around 11.3 to 12.8

ohiojim · Mar 5, 2009

did someone say a cellar 'MAY' be a bad place to charge a battery ???? not to mention the noxious fumes,..called hydrogen,..throw in a furnace pilot and you got one hell of an explosion

Hoosier Pete · Mar 5, 2009

Use a battery hydrometer to evaluate the state of charge. 1260 specific gravity is good.
Pete

El Toro · Mar 5, 2009

You should use a hydrometer and check the specific
gravity of each cell on each battery and compare the readings. A fully charged battery should have a reading of around 1.280. If one cell reads a lot lower than the others means you have a weak battery cell and will probably cause battery failure later. Hal

Stovepipe · Mar 5, 2009

You should charge it overnight on low, in a well ventilated area. Then get it load tested to see if the battery is good.

HENRY E NC · Mar 5, 2009

In my years of battery usage, (had a large boat that had three banks of batteries, some lead acid, some gel cells and some AGM) Most batteries are fully charge at 13.9 and many Alternators put out 14.2 to 1 4.7 so if the car is running it will iindicate in the 14 range. I currently have some AGM in cars that stay fairly constant and le
ad acid that vary some. A slow 4-6 amp chage will do more for a battery than a 10 amp charge. Henry

mEl · Mar 6, 2009

While I agree that the hydrometer is the proper way to evaluate a battery most nowdays are sealed maintanance free and are not servicable as older designs were. If a battery tests below 12.2 Volts it is discharged badly as even a low battery will test normal voltage with no load. mEl

Billy NY · Mar 6, 2009

I use one of those meters with a load switch, without putting a load on it, it will read 12 volts or so, flip that switch for a second and watch the needle dip, and that will tell you whether it's charged or not, if it dips too far, battery is often times N/G, once in awhile you can bring one back, one handy tool to have, also use it to check the charging system while its running.

Handsome Jim · Mar 9, 2009

god bless

battery voltage

Bill from MA

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John T

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buickanddeere

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ken in texas

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Allan in NE

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Anonymous-0

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ohiojim

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Hoosier Pete

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El Toro

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Stovepipe

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HENRY E NC

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mEl

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Billy NY

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Handsome Jim

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