Battery Pooched? Has 12.7V but wont start car - Honda-Tech

Battery Pooched? Has 12.7V but wont start car

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Old 05-08-2007, 10:00 AM   #1
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Default Battery Pooched? Has 12.7V but wont start car

Came back from a weekend vacation to where I parked my car and the battery was dead. No power. Boosted it and drove home, when I got home (15min drive) I turned off the car and tried to turn it on to see if the battery was charged. No dice, didnt have enough juice to start the car.

Boosted it again and went for a high rpm rip on the highway, came back, and the battery was now fully juiced, car started hard no problems.

Left it overnight until today and I came out to a another dead battery, had power, but not enough.

So I throw the voltage tester on it and sure enough, 12.6-12.7V

Boosted it with a good battery then connected the dead battery and never turned the car off (just pulled off connections and connected dead batt)

Then I checked the voltage while running. 14.7VOLTS!!!! WTF!!

So whats going on here?

-its got 12.6V but wont star tthe car
-another battery with 12.5V starts it no problem
-alternator charging it good @ 14.7V

Batteries only a year old and I dont think I got the reciept anymore
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Old 05-08-2007, 10:03 AM   #2
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Default Re: Battery Pooched? Has 12.7V but wont start car (W O T)

Sounds like something is draining your batt and draining it badly. Try jumping it and letting it idle for a while. Turn off the car and disconnect both power and neg. from the batt. and leave it for about 5 mins and then check the reading (do before you pull and after). If the reading changes then its a defaulty batt. If it stays the same then its something draining.


After the jump you read 14.7v, after the 5 mins you read 14v, batt. is good. If you come back and read 12v batt is bad.
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Old 05-08-2007, 10:12 AM   #3
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12V at the battery with no load is not necessarily a bad battery.typical automotive battery is 2.2V per cell, with 6 cells present. 13.2 at rest but every car has a little load on the battery at all times. (ECU memory, radio memory, etc) so a 12-12.6 rading is far from unreasonable.

the main thing is what does the voltage do when you start the car, or even switch on the lights. (ie apply load)
Flip the headlights on, initially the voltage will drop slightly then should hold around 12V, if it drops >~1V per 15-30 seconds after the voltage stabilizes, then it's time for a new battery.

bad battery, bad connections to battery, starter wire defective, bad starter... all of wihich will cause this problem.
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Old 05-08-2007, 10:17 AM   #4
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Default Re: (Relic1)

Ya I figure 12.6V was good, I just dont get why it says the battery has that voltage but wont start the car

Then swap in a battery with the same voltage, and the car starts first kick

I'll check for parasitic loss later as Im at work now, I just dont get why the battery isnt keeping a charge or not using the charge that it has
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Old 05-08-2007, 10:36 AM   #5
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is it an Optima yellow top by any chance?

i had that measured 13volts, but when i connected it to a volt meter and touched it to a spare starter, the battery would actually drain down to 8volts output. it was fried, and i was choked cuz i thought my starter was dead and bought a new one...
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