Battery gauge fluctuations: normal?

Joined
Sep 24, 2006
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Philippines
I have dual battery setup. With engine off, battery level is exactly in the middle line (between the 0 - 18v scale). Upon startup with no A/C or other electrical accessories, the battery needle slowly rises and based on my calculation of the gauge, it sits around the 12v level.

This rising behavior from 9v to 12v is normal, right?

Now, when I turn on the A/C or heater or fog/head lights, the needle dips a little bit - probably around the 10-11v level. And on the A/C, the fan seems not be blowing more air as if it's lacking juice. When I turn off the headlights, needle goes back to its normal level and blower blows more air.

Now, this behavior is not normal, right?

What is probably the defect here: battery or alternator or both?
I don't have any crazy idiot lights on my dash right now. Batteries are about 3 1/2 years old from PO.

I did search but did not get something related to battery gauge fluctuations.

As usual, hope you can help I would know what needs to be checked/R&R.
 

Grench

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I'm -not- a mechanic.

Sounds like an alternator to me. My truck runs @ 15 volts on the dummy meter in the cab steady as a rock. If it were the voltage regulator, it would hop to 18. If it were the battery, it would still pump @15 when running.

When you did your dual battery system, did you set up the alternator sending/signal wire right? It kind of sounds like the alternator may not be getting signal to switch into charge mode.
 

e9999

Gotta get outta here...
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measure the voltage at the battery, easy with a little voltmeter.
there are tables out there for voltage vs temperature. Should be around 12.5V or so at rest, and a bit over 14V when running IIRC
 
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Dual battery setup is stock - mine is a JDM with an electric winch.

Will check battery voltages this weekend.
 
Joined
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How old are your batteries ? If your lights and other electricals dim at idle it's probably time to look for new ones. You can expect to wake up one morning and be unable to start the engine in a short amount of time.

If your batteries are fresh, the alternator is the next suspect.

Most times it's the batteries.


Kalawang
 
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Batteries are about 3- 1/2 years close to 4 years old.

Am planning on changing them this weekend. dual batt setups are expensive!!! I would need to replace both with almost identical ones.

all - thanks for the advise. Will see what happens later after battery replacement.
 

FloridaFJ80

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I have a volt meter on my rig it is plugged into my factory 12v outlet, it runs constantly at 13.6v sometimes fluctuating by +-.2 volts. I have a dual battery setup with a marine 3 way switch in between, i run constantly in the 1+2 switch on the marine switch. There have been two times where i start my rig and i am not getting any charge from my alt, the red light on the top right of the dash stays on and the a few other light stays on.. what could this be???? I then shut it off and restart the truck and it is all fine, is my alt giving out. I am running to batteries with different ages, one is a normal starting battery and the other is a marine deep cycle starting battery.
 
Joined
Jan 25, 2005
Messages
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Location
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Batteries are about 3- 1/2 years close to 4 years old.

Am planning on changing them this weekend. dual batt setups are expensive!!! I would need to replace both with almost identical ones.

all - thanks for the advise. Will see what happens later after battery replacement.

Don't be so eager to spend. Take the car to the battery shop and have a load test done. It's free, just be sure you know how to do your own readings or you could end up buying new batteries before you need them.


Kalawang
 

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