Battery Voltage Drops To 10v With Key On, 8.5 While Attempting To Crank - General DIY Discussions - DIY Chatroom Home Improvement Forum
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Old 01-04-2016, 09:24 PM   #1
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Battery voltage drops to 10v with key on, 8.5 while attempting to crank


Hey guys, need some help with my winter beater and dont know where to start with this one. Out of the blue yesterday the battery was dead, got a boost from a co-worker and it started up fine and got me home.

I tried to start it this morning paying attention to the voltmeter and noticed it had 12+ volts before I did anything, I stuck the key in and turned it to ON where the pump primes, and the voltage dipped to 10.2 or so and the lights and cluster went dim, I tried to crank knowing it wouldnt work but the voltage dropped to 8v and the starter did not even attempt.

I connect my battery charger to it and it basically goes into maintain mode as it thinks the battery is fully charged and I cant override that.

Unfortunately this car uses an AGM battery but I tried my spare and it did the exact same thing.

Could this be an ignition switch thing? Short? How would you guys start diagnosing this? It starts right up with a boost. It is a 2002 Infiniti Qx4 suv btw

Thanks alot!
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Old 01-04-2016, 09:29 PM   #2
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Clean all your battery terminals and connections. Then retest. Slight chance you have corrosion interfering with electrical flow.
If it still tests bad then replace battery.

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Old 01-04-2016, 10:48 PM   #3
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Sounds like a bad battery to me. Take it out and take to Canadian Tire and have them test. I think they still do it for free. Charge it as much as you can first.
There is a possibility it is a charging system problem draining the battery. What did the voltage go to when the car started? 13.5-14 is good for charging. Much higher and you overcharging and damaging the battery. No change in voltage and system is not charging.
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Old 01-05-2016, 02:46 AM   #4
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They wont test the battery because of its design, it has threaded holes for the terminals instead of external studs or posts so they say there tester will not connect to it.

I do have another battery, which is the exact same battery, but from another audio car I scrapped, and it does the same thing. They are both 5+ years old, but very high quality, what are the odds both died here

Voltage is 14.5v when running, I cleaned the connections at the battery, but not at the body part of the grounds
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Old 01-05-2016, 04:07 AM   #5
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Quote:
Originally Posted by KevinEF7 View Post
They wont test the battery because of its design, it has threaded holes for the terminals instead of external studs or posts so they say there tester will not connect to it.

I do have another battery, which is the exact same battery, but from another audio car I scrapped, and it does the same thing. They are both 5+ years old, but very high quality, what are the odds both died here

Voltage is 14.5v when running, I cleaned the connections at the battery, but not at the body part of the grounds
That is an excuse if they are stating that they will not test it, because your terminals use the bolts to hold the cables on to the battery. Find a mom & pop garage. Most likely your alternator is the culprit along with the battery, if those two items have never been replaced, since you are stating that the battery is dropping while driving. So that means that the battery would not be charging.

You can get a real Amp meter from any Napa store or order it online and mount somewhere on the dash.



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Old 01-05-2016, 05:44 AM   #6
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Sounds like a dead/weak battery, not holding charge. If the second battery has been setting for a long time. It probably had/has very little charge left in it also.
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Old 01-05-2016, 07:02 AM   #7
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Just to be clear once the car is running it runs perfect, no lights are dim, voltage is steady @ 14.5 volts which is perfectly normal. The alternator is about 2 years old but is an OEM part, I have no fear its the alternator.

It just seems weird that as soon as you put the key to ON, so say the fuel pump primes, abs and ecu relay get power, that alone drops the battery voltage quite a bit for some reason, and then as soon as I turn the key to start, the voltage drops even more instantly.

If I have to replace the battery I will, but its not a part store battery, I have to order this, unfortunately my wiring is all configured to accept this battery. Seems odd both could fail the very same way on the same cold night though.

Theres no way an ignition switch or some other short could cause such a weird issue but be perfectly fine when given a jump start from another running vehicle? If the batteries were toast, would I have been able to drive the 50 miles home after getting that jump start?
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Old 01-05-2016, 09:16 AM   #8
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Sounds like a dead battery to me.

I find it hard to believe they can't test the battery because of the terminals. Probably half the batteries made these days have those terminals.
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Old 01-05-2016, 09:42 AM   #9
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Before replacing the battery, check the grounds, also have it load tested. Odds are it's the battery, seems odd they won't load test it.
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Old 01-05-2016, 03:16 PM   #10
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Kevin I had an issue with a Buick, that the connection at the end of the Positive, was actually corroding. They used layers to make up that piece. So after a while it got so bad, I just chopped it off and put on a new end.

The battery drain could also be caused by a stuck relay or Vampire that is causing the battery to drain to the chassis, which is caused by wiring that the insulation has worn off. You never get shocked from it. It just happens when the car is off.



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Old 01-05-2016, 05:09 PM   #11
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this is not a special battery, a lot of gm use that type of connection, they can be purchase anywhere they sell car battery
if car starts ok with boost then your battery is dead or have a bad ground connection
if your budget is low go to a car junk yard and find a similar used one, they should be already charged and tested
for your spare, if it has been not charged for several month, it is now dead
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Old 01-05-2016, 09:06 PM   #12
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Quote:
Originally Posted by KevinEF7 View Post
Just to be clear once the car is running it runs perfect
After it starts, its not using the battery at all.
You might even have 12V on the battery when the engine is off, but when you try to start the car, there is a big load on the battery and the voltage drops.

So Canadian Tire can't dig up a couple of bolts to put in the terminals to test it? You just had the misfortune of talking to a no-mind. What do want for minimum wage. If you have another Canadian Tire in the area take it there, or another time of day when somebody else is at the counter.

If the battery is more than 6 years old, myself, I would just assume its the battery from what you described, and buy a new battery.
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Old 01-06-2016, 08:58 PM   #13
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Took 3 places to find a similar size battery with threaded studs for terminals, but new battery fixed it, thanks guys
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