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Old 05-17-2019, 03:29 PM   #1
fanatichuman
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Battery voltage seems really low

Hey guys,

In the past days I did some pa soft reprogramming. Each time my car's battery was 11.4-11.5 V, which seems extremely low. I also think I get some low voltage related error codes.

I want to hook up a battery charger/tender over night to see how the voltage behaves afterwards. Where should I hook up the tender? At the posts under the hood, or should I take the battery out and hook the tender directly to the battery?

Cheers,
fanatic

Edit: the car (seems) to start fine despite the low V.

Last edited by fanatichuman; 05-17-2019 at 03:35 PM.
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Old 05-17-2019, 05:43 PM   #2
shadetreemech
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My battery has been 11.7 to 11.8 volts for several years. Alternator voltage exceeds 14 volts. That is measured by several different digital volt meters at the battery. I took the battery out of the car and took it to a local parts house. They tested it pronounced it good but 'needs a charge'. They charged it. I checked the 'parasitic drain' and it was under 30 ma, normal. Two weeks later it was back to 11.7 volts. Car starts every time even after sitting for 7 weeks. Oh well. At the first hint of a 'hard start' or funny cautions I will replace it. My habit, in order to protect the rest of the electronics, is to disconnect the positive terminal when charging a battery in the car. If you take the battery out of the car do not set it on concrete.

Cheers
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Old 05-17-2019, 05:46 PM   #3
fanatichuman
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Quote:
Originally Posted by shadetreemech View Post
My battery has been 11.7 to 11.8 volts for several years. Alternator voltage exceeds 14 volts. That is measured by several different digital volt meters at the battery. I took the battery out of the car and took it to a local parts house. They tested it pronounced it good but 'needs a charge'. They charged it. I checked the 'parasitic drain' and it was under 30 ma, normal. Two weeks later it was back to 11.7 volts. Car starts every time even after sitting for 7 weeks. Oh well. At the first hint of a 'hard start' or funny cautions I will replace it. My habit, in order to protect the rest of the electronics, is to disconnect the positive terminal when charging a battery in the car. If you take the battery out of the car do not set it on concrete.

Cheers
So, I gather I should disconnect the posts and charge with the tender directly at the battery.

How did you check for parasitic drain?

Cheers
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Old 05-17-2019, 08:39 PM   #4
Sapote
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Quote:
Originally Posted by fanatichuman View Post
So, I gather I should disconnect the posts and charge with the tender directly at the battery.

How did you check for parasitic drain?

Cheers
Just leave batt untouched and connect the charger to the front RH fender posts.

No need to check batt drain unless you believe batt drained too fast problem.

Normal battery should be above 12.6V engine off, and around 14V engine idling, measured on batt posts directly.

Short trip driving not enough charging time?
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Old 05-17-2019, 10:15 PM   #5
jmo69
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I hook my tender up directly to the battery without disconnecting it.
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Alternative to expensive xi control arm bushings https://forum.e46fanatics.com/showthread.php?t=1231503

Bad outer xi ball joint? https://forum.e46fanatics.com/showthread.php?t=1127077


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Old 05-17-2019, 10:56 PM   #6
fanatichuman
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Quote:
Originally Posted by Sapote View Post
Just leave batt untouched and connect the charger to the front RH fender posts.

No need to check batt drain unless you believe batt drained too fast problem.

Normal battery should be above 12.6V engine off, and around 14V engine idling, measured on batt posts directly.

Short trip driving not enough charging time?
Jeah, i guess. 5 min to and back from work, and some longer trips on the WE. Trying to figure out whether my bat is bad or just never got fully charged.
Thanks,
Fana

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Old 05-19-2019, 12:09 PM   #7
shadetreemech
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Quote:
Originally Posted by Sapote View Post
Just leave batt untouched and connect the charger to the front RH fender posts.

No need to check batt drain unless you believe batt drained too fast problem.

Normal battery should be above 12.6V engine off, and around 14V engine idling, measured on batt posts directly.

Short trip driving not enough charging time?
If I have a proper battery charger I agree. I don't know what some of these cheap Chinese battery tenders are. A friend of mine looked at the output of one with an oscilloscope and said it was a half wave rectified square wave. A battery will care less but some of the electronics might not like it.

Does anyone have any experience with these battery tenders?
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Old 05-19-2019, 02:01 PM   #8
CalVol
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I have a one-year old Bosch AGM battery and it consistently reads 12.1-12.2v using the instrument cluster with the car being driven about 2x/week. Alt output is 14.0-14.1v. I bought a cheap $10 Stanley battery tender and it keeps it charged at 12.6v. I tested parasitic draw and it was about 30ma. If I take the battery tender off for a few days, the voltage drops back down to 12.2v, so I guess it's just a shitty battery.

Last edited by CalVol; 05-19-2019 at 02:39 PM.
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Old 05-19-2019, 06:31 PM   #9
jdstrickland
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You can connect the charger wherever you want, engine bay or trunk. No difference. A caveat is that the fasteners (screws) in the charging system must all be securely tightened. If not tightened, it still doesn't matter where you connect the charger because the entire system will be compromised and any voltages you get will be unreliable.

DISCONNECT THE NEGATIVE BATTERY TERMINAL SO YOU DO NOT TURN YOUR TOOLS INTO AN ARC WELDING ROD

There is a fat red wire on the back of the alternator that goes to a post on the starter that is shared with another fat red wire that goes to the terminal in the engine bay for the + connection (B Post) of the charger/jumper cables. From there, the fat red wire goes to the battery.

Check that the nuts on the underside of the B Post, the starter, and the alternator to be sure they are all tight. I had trouble once with the B Post that was not tightened properly.

Voltage on a static battery ought to be 12.6 volts. When the engine is running you should see 14.4 volts. A variance of 0.1 or so can be from the tester, but if you are seeing a variance of about 0.5 or more, then you should consider a malfunction, but certainly get another tester first. Use your tester on another car that is not giving trouble to confirm that your tester is giving bad intelligence.
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Old Yesterday, 02:51 AM   #10
fanatichuman
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Quote:
Originally Posted by jdstrickland View Post
You can connect the charger wherever you want, engine bay or trunk. No difference. A caveat is that the fasteners (screws) in the charging system must all be securely tightened. If not tightened, it still doesn't matter where you connect the charger because the entire system will be compromised and any voltages you get will be unreliable.

DISCONNECT THE NEGATIVE BATTERY TERMINAL SO YOU DO NOT TURN YOUR TOOLS INTO AN ARC WELDING ROD

There is a fat red wire on the back of the alternator that goes to a post on the starter that is shared with another fat red wire that goes to the terminal in the engine bay for the + connection (B Post) of the charger/jumper cables. From there, the fat red wire goes to the battery.

Check that the nuts on the underside of the B Post, the starter, and the alternator to be sure they are all tight. I had trouble once with the B Post that was not tightened properly.

Voltage on a static battery ought to be 12.6 volts. When the engine is running you should see 14.4 volts. A variance of 0.1 or so can be from the tester, but if you are seeing a variance of about 0.5 or more, then you should consider a malfunction, but certainly get another tester first. Use your tester on another car that is not giving trouble to confirm that your tester is giving bad intelligence.
Great advice, thanks!

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