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What voltage should a car battery be at?

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Old 06-10-08, 12:04 AM   #1
HarrierRX300
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Default What voltage should a car battery be at?

Hello,
I was wondering what voltage my car should be at? I tried to start it one day and it made some clicking noise as if it's not enough battery charged. I haven't driven my car in a month so I'm guessing the batterie's dead. I charged it and the volt meter shows 13.4 volts. When it's charging and the cars running, it shows 14.5 volts. Is 13.4 volts enough long term or should I buy a new Lexus battery. And if I did buy a new battery and I swapped it out, will disconnecting the battery reset any clock or settings in the car? Thanks...
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Old 06-10-08, 01:24 AM   #2
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Search the term battery and you will have lots of advice.

I would start by charging the battery overnight. If it revives then you need not buy a new battery.

Battery are some what a generic part. Since the markup is high at delaership, you would do lot better in buying on your own (unless it being covered by the warranty).


Voltage measurement is typically not a good test for battery. You have to test it under load (free service provided by most places that sell a battery).


If you have every thing preplanned, the swap can be done so quick that you will not loose any setting.

Salim
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Old 06-10-08, 04:22 AM   #3
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I'm suspicious of your voltmeter. With the engine not running, a car battery will have a voltage reading of 12 volts (that's why they call it a 12 volt battery). The normal charging voltage (voltage with engine running) is about 13.6 volts. It could be a little over this, but over 14 volts seems too high to me.

I agree with what Salim wrote too. Driving around for a while (if your charging system is working OK) should give a full battery charge as well as overnight on a battery charger.

My experience is that, unless you use one of the 9-volt battery backup techniques, you will have to reset the clock and maybe some of the memory settings when you disconnect the battery. I guess I'm not as fast as Salim.

My view is that age does matter. If your battery is over 5 years old and you are having any symptoms that point to the battery, I'd be inclined to replace the car battery.
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Old 06-10-08, 09:24 AM   #4
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Correction .. yes the clock is the only thing that will be reset when you do a quick swap.

Radio, seats and ECU stored information needs a minute or two (not measured).
I am most picky about my seat position so I make sure it is set in the position I like and then disconnect the battery. When I reconnect, I store the last position as mine (without moving the seat). Garage door opener seems not affected by loss of 12v.

One more thing ... please make sure the key is removed from ignition during the whole process. I read some where that the air bag deployed sensor gets activated (may have been SC) better safe than sorry.

Salim
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Old 06-10-08, 11:24 AM   #5
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Thanks everyone. I did charge the battery overnight and everything seems fine. I'll drive it this coming weekend to circulate the oil as well as charging it while driving. The weird thing is. My gas needle was at the half mark. I had an emergency gas tank I just filled last week in the garage so I filled it. I started the car and the needle was still at half. I knew my gas tank was full since I didn't drive it so I drove to the gas station and tried to fill it. It stopped at $1.00 with overspill. I went into the gas station and asked the attendant to look at my car since my needle was at half. He tried pumping gas and gas spilled out. It was full. I asked him to take a look and when he started the car, it was at FULL. Does it have anything to do with the angle of the gas pump resetting the gas needle? Weird...

All in all, car is fully charged and gas is full... Nothing is wrong... Double weird...
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Old 06-10-08, 04:46 PM   #6
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There is no calibration for gas. I am assuming that like typical gauge, the float acts like a voltage divider and sends the signal to the gauge. Assuming the battery was weak, the gauge will show less than what the actual level will be.

Having a good battery is now a must for all gauges and sensors.

Salim
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Old 06-13-08, 12:33 AM   #7
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Quote:
Originally Posted by bob2200 View Post
I'm suspicious of your voltmeter. With the engine not running, a car battery will have a voltage reading of 12 volts (that's why they call it a 12 volt battery). The normal charging voltage (voltage with engine running) is about 13.6 volts. It could be a little over this, but over 14 volts seems too high to me.

I agree with what Salim wrote too. Driving around for a while (if your charging system is working OK) should give a full battery charge as well as overnight on a battery charger.

My experience is that, unless you use one of the 9-volt battery backup techniques, you will have to reset the clock and maybe some of the memory settings when you disconnect the battery. I guess I'm not as fast as Salim.

My view is that age does matter. If your battery is over 5 years old and you are having any symptoms that point to the battery, I'd be inclined to replace the car battery.
Full charge on a 12v battery is 12.6-12.8 volts. (2.1v per cell) Technically speaking a battery is virtually dead at 12v. I realize it will probably start the car and you won't know that it is nearly dead but it will have a very short life if it is run at 12v. I load tested my grandaughters battery when I was on vacation and it tested 13v., which is extremely high (I have seen 15-20% as high as 12.8 but have rarely ever seen one at 13v.) It tested very strong with not a lot of drop under load so the battery must normally run at that, but that high is unusual. GM cars normally run about 13.8v at about 1600- 1700 rpm but Ford normally run 14v.-14.4v. at that rpm. I prefer to see it on the higher end, actually up to 15v. is CONSIDERED normal but is higher than I like to see it. I have driven Ford trucks for many years and they have all run around 14.4v at 1600-1700rpm. (not at idle)
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Old 06-13-08, 04:33 AM   #8
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I stand corrected on some of what you write (ref. http://www.arttec.net/Solar_Mower/4_...20Charging.pdf ). My experience goes back to electro-mechanical voltage regulators, where the upper charging voltage was electro-mechanically limited to around 13.6 volts.
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Old 06-13-08, 04:43 AM   #9
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Another reference http://www.buchanan1.net/lead_acid.shtml on battery voltage vs. temperature w/o load.
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Old 06-14-08, 12:25 AM   #10
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Quote:
Originally Posted by bob2200 View Post
I stand corrected on some of what you write (ref. http://www.arttec.net/Solar_Mower/4_...20Charging.pdf ). My experience goes back to electro-mechanical voltage regulators, where the upper charging voltage was electro-mechanically limited to around 13.6 volts.
Bob- Some interesting reading. I have a great deal of tech material on batteries from many different sources and all types of batteries but most of what I wrote was from toooo many years of experience with batteries. My experience has been sometimes a little different than the tech stuff stated, but most of it was fairly close. I worked for Ford dealers for a # of years and have driven Ford trucks for a lot of years- having had a '95,'99,'02 & currently have a '04. Ford for MANY years used batteries made by Gould National Battery, one of the best batteries ever built. They typically tested 12.8v- and lasted twice as long as anyone elses batteries (American). But in about '03 or so they sold to Excide and now are pretty much junk. Most Japanese cars (especially those made in Japan) use better batteries than we do here. I have seen enough odd (doesn't fit the mold) variations with batteries to write a book about.
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Old 06-14-08, 12:25 AM
 
 
 
 
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