Battery gauge reading low: Old battery died and still reads low with new battery - JeepForum.com

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post #1 of 17 Old 08-27-2009, 10:48 AM Thread Starter
jatepper
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Battery gauge reading low: Old battery died and still reads low with new battery

I was driving to work this morning and noticed the battery gauge (factory gauge) was reading only about 10V. Sure enough, when I went to the gas station to get my morning big gulp it would not start back up and had to get a jump. I went to NAPA and had them analyze my battery and it was dead. I bought a new optima, put it in, and gauge still reads low, but jeep cranked right up. Yesterday I had no problems with the gauge and I dont think it is coincidence I needed a new battery on the only day I realized my gauge was reading low.

Anyone have any info on this?


1986 CJ7 Laredo - Auto 14k miles
1985 CJ7 Renegade - Auto 33k miles
1982 CJ8 Scrambler - T5 T-SPD
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post #2 of 17 Old 08-27-2009, 11:05 AM
texasdave
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Gauges are inaccurate. Test your batery with a multi-meter to get a true reading and compare it to the gauge. The battery with out the engine running will register 12 volts or more. However, it doesn't measure the amperage and many times you can have voltage without sufficient amps to crank. When running your reading should be 14 volts or so which is measuring the output from the alternator, again use your multimeter to check the voltage at the battery and compare it with the gauge
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post #3 of 17 Old 08-27-2009, 11:08 AM Thread Starter
jatepper
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What I dont understand is that is was working perfectly fine yesterday. I personally think something is causing a draw on the battery when the jeep is on. Just noticed low gauge today and today battery was dead. This is "too coincidental" for me.

1986 CJ7 Laredo - Auto 14k miles
1985 CJ7 Renegade - Auto 33k miles
1982 CJ8 Scrambler - T5 T-SPD
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post #4 of 17 Old 08-27-2009, 11:26 AM
CSP
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The gauge isn't just the battery. It is the available voltage in the electrical system, including what the alternator is providing.

Sounds to me like your alternator has crapped out and the battery power is being drawn down as the engine is running. The voltage provided by the battery will only last so long if the alternator isn't working.

NAPA should have done a complete electrical system diagnosis before selling you a battery. It very well could be that the old battery was fine, but discharged. If they didn't attempt to put it on a charge and just checked the voltage it had, their test was incomplete.
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post #5 of 17 Old 08-27-2009, 11:37 AM Thread Starter
jatepper
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Quote:
Originally Posted by CSP View Post
The gauge isn't just the battery. It is the available voltage in the electrical system, including what the alternator is providing.

Sounds to me like your alternator has crapped out and the battery power is being drawn down as the engine is running. The voltage provided by the battery will only last so long if the alternator isn't working.

NAPA should have done a complete electrical system diagnosis before selling you a battery. It very well could be that the old battery was fine, but discharged. If they didn't attempt to put it on a charge and just checked the voltage it had, their test was incomplete.
This sounds more realistic. Do you know of a good replacement alternator or should I just buy one at the parts counter. I have a winch and I am going to have dual batteries as well.

Thanks.

1986 CJ7 Laredo - Auto 14k miles
1985 CJ7 Renegade - Auto 33k miles
1982 CJ8 Scrambler - T5 T-SPD
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post #6 of 17 Old 08-27-2009, 11:42 AM
CSP
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Don't just go and buy one at the parts counter!

Have the electrical system tested to determine what the actual problem is first. Don't go by what someone else or you think it might be. You've potentially wasted money on a battery that you may not have needed, so stop shotgunning parts at what you think might be the problem. It could be as simple as a bad charge wire from the alternator to the battery or a corroded connection.

If it does turn out to be the alternator, a stock replacement will work fine. If you want to upgrade, there are numerous threads here that cover what alternators make good upgrades.
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post #7 of 17 Old 08-27-2009, 12:54 PM
wellmax
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when the gauge on my cj starts reading low voltage it is normally the alternator has gone bad.

pull the alternator and have it checked.
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post #8 of 17 Old 08-27-2009, 01:34 PM
RARECJ8
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first, buy a digital multi-meter. they are invaluable and will save you lots of grief in the future. Double check all connections between battery (+AND -) , starting solenoid, grounds and the like. Assuming they are all tight and clean, then with motor off, take a reading at the battery. should be like 12.4 or so. then fire the motor and check voltage at the battery. this time it should be about 14.7. If not, then the charging system is not working. Then pull the alt and take to a reliable battery shop. i don;t trust the tests done at vatozone, et al. The best test is where they actually put the alt on a scope to check the wave form, etc. If ur getting a good 14.7 or so, then problem is somewhere else. do you leave accessories on when rig is off? the dash clock for example will suck power.

glad to help, but need more information based on these tests.

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post #9 of 17 Old 08-27-2009, 02:42 PM Thread Starter
jatepper
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Quote:
Originally Posted by CSP View Post
Don't just go and buy one at the parts counter!

Have the electrical system tested to determine what the actual problem is first. Don't go by what someone else or you think it might be. You've potentially wasted money on a battery that you may not have needed, so stop shotgunning parts at what you think might be the problem. It could be as simple as a bad charge wire from the alternator to the battery or a corroded connection.

If it does turn out to be the alternator, a stock replacement will work fine. If you want to upgrade, there are numerous threads here that cover what alternators make good upgrades.
10-4. I didnt mean I was just going to buy one. I will have the electrical tested before doing so. I dont feel bad about buying the battery anyhow because it was made in 11-2003, so it was bound to die sooner or later anyway. That was my thought behind the battery purchase. Too bad it was not the problem, but glad I replaced it anyway.

1986 CJ7 Laredo - Auto 14k miles
1985 CJ7 Renegade - Auto 33k miles
1982 CJ8 Scrambler - T5 T-SPD
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post #10 of 17 Old 08-27-2009, 07:16 PM
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Heat kills batteries much faster than cold weather does...
Underhood heat, combined with a 23+ year old charging system could have caused all sorts of problems with the battery.

Since you had the charging system 'Analyzed', and they found no problems with the charging system, it was probably just battery failure.

With getting the charging system checked,
I would have told you to look for AC voltage (Diode out in the rectifier).
Batteries HATE AC Voltage!

I would have told you to look for electrolyte levels in the cells.
Dry cells sneak up on you QUICK in the summer months!

I would have told you to clean the terminals, and check the battery with a load tester to see if there was a shorted cell or broken bridge between cells.
You get voltage, so just a multi-meter or volt meter won't tell you what you need to know.
You have to LOAD the battery to see if it's making AMPERAGE.
If it's not, then you have a cell problem somewhere,
Broken bridge, shorted out or broken plate, scale shorting the plates out, ect.
-----------------

Could have been a number of things,

But I can tell you from my Starter/Alternator/Battery business days,
The 'Dog Days' of summer were my BEST SELLING TIMES!
Beat winter sales by 3 to 1!

Just remember,
If you deeply discharge that AGM battery you purchased,
You will have problems with it also...

AGM batteries use a Gel Electrolyte on the plates, then roll the plates to fit in the 'Six Pack' case.
That gel keeps the gas bubbles from escaping away from the plates,
And everywhere a bubble forms on the plate, that is a 'Dead' spot since the electrolyte is no longer in contact with the plate...

So make sure your alternator is working correctly and keeps the battery charged,
And don't discharge the battery deeply, like leaving lights on or radio on when not running...

The effects are cumulative, so the problem gets worse over time,
And those AGM batteries usually only have a 1 year warranty!
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post #11 of 17 Old 08-27-2009, 10:07 PM Thread Starter
jatepper
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Turned out to be that little stud on the back of the alternator where the power wire bolts on to. It was loose and damaged so bad then when I used the 10mm socket to take off the nut to remove the wire, the stud just broke in half. $49 for a new alternator and now I'm good to go.

1986 CJ7 Laredo - Auto 14k miles
1985 CJ7 Renegade - Auto 33k miles
1982 CJ8 Scrambler - T5 T-SPD
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post #12 of 17 Old 08-28-2009, 06:40 AM
JeepHammer
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Aren't intermittent 'Issues' so much fun!

Nothing like having a vehicle in the shop for two weeks,
Rattling, banging, prying, vibrating things to make a symptom show up...
And of course it doesn't hickup once for us...

Then return it to the owner, and two blocks away it quits on them!

Glad you found yours before it did any more damage!
I've got an alternator rebuild today myself.
Diode in the rectifier popped it's self in my full size and runs the battery down when it sets,
Throws AC voltage at my battery when it's running!

Oh joy, Oh Fun!
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post #13 of 17 Old 08-28-2009, 08:21 AM
CSP
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Quote:
Originally Posted by JeepHammer View Post
Since you had the charging system 'Analyzed', and they found no problems with the charging system, it was probably just battery failure.
That's not what was said. He said he had the battery analyzed and it was dead. There's no mention of the entire charging system being checked.

Glad you got it figured out jatepper!
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post #14 of 17 Old 08-29-2009, 03:16 PM Thread Starter
jatepper
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OK, I think I lied to you all. I replaced my alternator, which was good anyway because it was 24 years old and had a broken electrical connector. Anyhow, when I put my new alternator on, along with my new battery, my battery indicator gauge worked right away and was reading about 13V or so. Last night on my way to a poker game the gauge starting reading pretty low again. I am worried that for some reason there is some kind of fault in my electrical system not allowing my alternator to charge my battery.

Hammer, where are you man?

1986 CJ7 Laredo - Auto 14k miles
1985 CJ7 Renegade - Auto 33k miles
1982 CJ8 Scrambler - T5 T-SPD
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post #15 of 17 Old 08-29-2009, 09:24 PM
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