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Unread 09-15-2013, 05:35 PM   #1
Patrice01
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Join Date: Sep 2013
Location: Yellowknife, NWT
Posts: 2
Battery question

I hope this is in the right section of the forum (first post here! Hi)

Long story short, I often have a flat battery problem and need a boost (happened 3 times in 2 months)

First time I know it was my light still on. I just thought those turn off automatically, I guess I was wrong.
Second time it happen I don't know. I don't think anything was left on but I couldn't say for sure.
Third time I know for sure nothing was left on. The vehicle has just been sitting there for a week and when I tried to start it the battery was dead.

I played taking with my multimeter today. Here are the results so far:

1) with vehicle turned off I get a reading of 12.65 v
2) with vehicle turned off and light turned on I get a reading of 12.25 v
3) with vehicle turned on I get a reading that seem to go from 14.10 to 14.50

The result when turned on plus the fact the check battery light does not turn on tells me the alternator is ok. Am I right to come to that conclusion?

Anything else those results tells us? I do not know how old the battery is as I bought the vehicle 4 months ago. It does not look too old though.

Any info you can come up with to help me find the problem will be much appreciated. Thx

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Unread 09-15-2013, 06:17 PM   #2
JeepNicholson
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1996 ZJ 
 
Join Date: Apr 2013
Location: Burbank, OH
Posts: 755
Quote:
Originally Posted by Patrice01 View Post
I hope this is in the right section of the forum (first post here! Hi)

Long story short, I often have a flat battery problem and need a boost (happened 3 times in 2 months)

First time I know it was my light still on. I just thought those turn off automatically, I guess I was wrong.
Second time it happen I don't know. I don't think anything was left on but I couldn't say for sure.
Third time I know for sure nothing was left on. The vehicle has just been sitting there for a week and when I tried to start it the battery was dead.

I played taking with my multimeter today. Here are the results so far:

1) with vehicle turned off I get a reading of 12.65 v
2) with vehicle turned off and light turned on I get a reading of 12.25 v
3) with vehicle turned on I get a reading that seem to go from 14.10 to 14.50

The result when turned on plus the fact the check battery light does not turn on tells me the alternator is ok. Am I right to come to that conclusion?

Anything else those results tells us? I do not know how old the battery is as I bought the vehicle 4 months ago. It does not look too old though.

Any info you can come up with to help me find the problem will be much appreciated. Thx
Battery should have a date on it somewhere.

You can also check for parasitic draw by testing for amperage with your multimeter between the negative battery post and negative terminal (engine off), 25-50 mA should be ok, any more than that and you've got too much parasitic draw.
If there's too much draw, start pulling fuses until the excessive draw stops, then you'll know what system is causing it.
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Unread 09-15-2013, 08:33 PM   #3
Patrice01
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Join Date: Sep 2013
Location: Yellowknife, NWT
Posts: 2
Quote:
Originally Posted by JeepNicholson View Post
Battery should have a date on it somewhere.

You can also check for parasitic draw by testing for amperage with your multimeter between the negative battery post and negative terminal (engine off), 25-50 mA should be ok, any more than that and you've got too much parasitic draw.
If there's too much draw, start pulling fuses until the excessive draw stops, then you'll know what system is causing it.
Didn't check for the date on the battery yet. it's dark out. However I started investigating for parasitic draw and I might have something here. My electricity reading knowledge is kind of low so better check with you.

I get a reading of 0.13 when my multimeter is set to a 10A. That means 130 mA? right? If so, thats much higher than the healthy 25-50 mA you suggested.

Also I checked the voltage on the battery after 3-4h and now get 12.50 v instead of 2.65. is that something?

Thanks
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Unread 09-16-2013, 12:30 AM   #4
5-90
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1988 XJ Cherokee 
 
Join Date: Sep 2006
Location: San Jose, CA, Hammerspace
Posts: 5,339
Quote:
Originally Posted by Patrice01 View Post
I hope this is in the right section of the forum (first post here! Hi)

Long story short, I often have a flat battery problem and need a boost (happened 3 times in 2 months)

First time I know it was my light still on. I just thought those turn off automatically, I guess I was wrong.
Second time it happen I don't know. I don't think anything was left on but I couldn't say for sure.
Third time I know for sure nothing was left on. The vehicle has just been sitting there for a week and when I tried to start it the battery was dead.

I played taking with my multimeter today. Here are the results so far:

1) with vehicle turned off I get a reading of 12.65 v
Acceptable

Quote:
Originally Posted by Patrice01 View Post
2) with vehicle turned off and light turned on I get a reading of 12.25 v
Acceptable. In a closed system; voltage, current, power, and resistance are all mathematically related (cf: Ohm's Law, Watt's Law. The wiki pages on those two are good.)

Quote:
Originally Posted by Patrice01 View Post
3) with vehicle turned on I get a reading that seem to go from 14.10 to 14.50
A bit high, but some variation is normal. I'm more worried about the fact that you're consistently over 14.0VDC..

Quote:
Originally Posted by Patrice01 View Post
The result when turned on plus the fact the check battery light does not turn on tells me the alternator is ok. Am I right to come to that conclusion?
Vaguely. Your instruments are not always right, which is why you have test instruments to verify the readings.)

Quote:
Originally Posted by Patrice01 View Post
Anything else those results tells us? I do not know how old the battery is as I bought the vehicle 4 months ago. It does not look too old though.

Any info you can come up with to help me find the problem will be much appreciated. Thx
The date of purchase of the battery should have been punched out of the label on the top. The "date code" of battery manufacture is a separate sticker on the side, usually with a letter and a number (the letter represents the month, and the number is the last digit of the year. For instance, if I went and bought a battery right now, I'd probably get one coded G-3, for manufacture in August 2013. I check the manufacture codes on batteries before I plonk down dosh for them...)

However, I have posted a good "driveway test" for your primary electrical (battery, alternator, starter) that you can do with a helper in about 15 minutes, at home, with a DMM. While it's not a quantitative test (won't tell you actual alternator output current, for instance,) it is a useful quantitative test (will tell you if everything is keeping up with demands.) I haven't a link - but it's its own thread that I started - search for "Battery," "Starter," and "Alternator" in any combination you like, thread started by me. It should also have tips on what should be checked, if primary electrical issues are suspected...
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