Battery voltage question
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Instructor
Joined: Apr 2014
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From: Princeton NJ
Battery voltage question
I have a 2008 coupe that is a semi-daily driver. I drive it most days but sometimes it sits for a week or 2. I bought a battery maintainer to keep it in good shape when it's going to sit for a while. I periodically check the battery voltage with a multimeter and it is usually in the 12.3 to 12.5 range. Once it was up to 12.7 but that's tops. Is this acceptable? I should say that I never have a problem starting the car -- just a little paranoid after reading about all the battery failures.
Thanks
Thanks
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From: Hudson WI
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From: Southern Utah
Race Director
Joined: Aug 2005
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From: Hudson WI
NCM Sinkhole Donor
True, but an accurate measure is right at the battery with the negative terminal disconnected from the car. Depending on the car, the draw on the battery can make it appear lower than it really is. The DIC voltage is only valid when the car is running. If the engine is not running, the car's systems are drawing significantly when the DIC is available.
Thread Starter
Instructor
Joined: Apr 2014
Posts: 176
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From: Princeton NJ
So it's tough to get a real accurate reading. Temperature is a factor and it's impractical to routinely disconnect the battery just to keep an eye on it. I guess I'll just assume the range I'm getting is OK.
Thanks for the quick responses.
Thanks for the quick responses.
Team Owner
Joined: Mar 2008
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From: Southern Utah
GM has a 45 day stand test that the battery has to pass, so based on what he said, the battery is not getting fully charged. Trust me, I had 4 battery engineers working for me when I sold batteries to the car companies. The receiving SOC was 12.75 and the car had to have 12.65 when it left the plant.
Thread Starter
Instructor
Joined: Apr 2014
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From: Princeton NJ
I have not checked the voltage with the battery disconnected. I'll try that tomorrow to see how different the reading is.
Thread Starter
Instructor
Joined: Apr 2014
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From: Princeton NJ
I hooked up the negative cable again and the voltage dropped to 12.40. I guess reconnecting the battery caused some systems that were sleeping (my technical term) to wake up and it took some power to do that. Also note that I did not have a fob with me because I didn't want to wake up anything else during the test.
So I'm not sure what all this means except that when I'm not going to drive the car for a week or 2 the battery maintainer is good insurance against having to call roadside assistance.
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Team Owner
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From: Southern Utah
There is still a surface charge on the battery if you check it immediately after removing the tender. In this case, 12.48 is too low. I believe the battery is bad. A good battery, charged and then left to sit for a couple of hours to get rid of the surface charge, should be right around 12.80. You are exactly correct about the car waking up and dropping a load on the battery which pulled it down a bit, but it didn't start out high enough in the first place before the computer woke up.
Thread Starter
Instructor
Joined: Apr 2014
Posts: 176
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From: Princeton NJ
There is still a surface charge on the battery if you check it immediately after removing the tender. In this case, 12.48 is too low. I believe the battery is bad. A good battery, charged and then left to sit for a couple of hours to get rid of the surface charge, should be right around 12.80. You are exactly correct about the car waking up and dropping a load on the battery which pulled it down a bit, but it didn't start out high enough in the first place before the computer woke up.
Thanks for your help.