DX.com
Results 1 to 11 of 11

Thread: 12v. car batteries ... resting voltage ? When to replace ?

  1. #1
    Flashaholic* TooManyGizmos's Avatar
    Join Date
    Jan 2006
    Location
    Humid Florida , USA
    Posts
    3,072

    Default 12v. car batteries ... resting voltage ? When to replace ?

    What should the resting voltage of a 12v. car battery be , 2 hours after driving the car 8 miles ?

    I think when bought new , the voltage is 12.70 volts.


    What resting voltage would be a hint the batt. is about to fail , and should be replaced ?

    Or can this only be determined by a cranking/amp test at a dealership or battery seller ?

    I realize age and heat are a factor too , but some seem to last years longer than others. I'm also not sure the Brand name assures longer life either. On some batteries you can't even check the electrolite level or top it off.

    Is it best just to replace every 4-5 years , no matter what , so you don't have a sudden no-crank failure ?
    .
    ~ "She" says ... ... I have ... TooManyGizmos ~

  2. #2
    *Flashaholic* Mr Happy's Avatar
    Join Date
    Nov 2007
    Location
    Southern California
    Posts
    5,390

    Default Re: 12v. car batteries ... resting voltage ? When to replace ?

    This reference should give you some info: http://www.batteryuniversity.com/partone-13.htm

    Basically you want the battery to read 12.6 V or higher after resting if it is to be in good condition and fully charged. As with most batteries I don't think you can get the whole story about condition without doing more elaborate load tests on it.

    (If you have your car serviced regularly by a competent workshop they should automatically test your battery and tell you when it needs replacing. A replacement every 5 years would not be unusual.)
    Last edited by Mr Happy; 10-29-2009 at 06:57 AM.

  3. #3

    Default Re: 12v. car batteries ... resting voltage ? When to replace ?

    A good battery should be between 12.4 to 12.6v at rest, it will drop some if any accesories are on (lights, radio, phone or gps chargers, flashers, etc) if you have an automotive voltage/amperage tester available, you can do a load test on the battery (hook it up and load it by 1/2 the cca rating of the battery for 15 seconds) if it drops below 10v, it's time for a new battery. Most autoparts stores can do this test for you, but beware, if they don't know what they are doing, they could test it as needing replacement when it does not. Also, the test must be done fully charged. Also, after testing it will be mostly dead and unable to start your car, requiring a recharge.

    Source: me, automotive tech student, only need another few shop hours to be certified.

    Good luck!
    I remember when I thought a 1w 45 lumen luxeon was bright...

  4. #4

    Default Re: 12v. car batteries ... resting voltage ? When to replace ?

    Yes it is best to replace every 4-5 years, your cost/year doesn't go up much trying to squeeze an extra year out of it, though if you drive the car nearly every day and it doesn't drop much below freezing in the winter where you live and the battery is large high-capacity per the vehicle (engine) size, it is possible to go a little longer but the first time it doesn't start you'll wish you just spent the money.

    This is especially true when better batteries tend to have a pro-rated warranty longer than 4 years so you aren't losing much money at all replacing it, so long as they take it instead of telling you it's good still.

  5. #5
    Flashaholic* TooManyGizmos's Avatar
    Join Date
    Jan 2006
    Location
    Humid Florida , USA
    Posts
    3,072

    Default Re: 12v. car batteries ... resting voltage ? When to replace ?

    Seems like very good and educated answers ..... thanks .

    Could be helpful to others , too .
    .
    ~ "She" says ... ... I have ... TooManyGizmos ~

  6. #6
    Flashaholic*
    Join Date
    Oct 2008
    Location
    Waikato, New Zealand
    Posts
    1,629

    Default Re: 12v. car batteries ... resting voltage ? When to replace ?

    Quote Originally Posted by J_C View Post
    Yes it is best to replace every 4-5 years, your cost/year doesn't go up much trying to squeeze an extra year out of it, though if you drive the car nearly every day and it doesn't drop much below freezing in the winter where you live and the battery is large high-capacity per the vehicle (engine) size, it is possible to go a little longer but the first time it doesn't start you'll wish you just spent the money.
    I have to agree totally with this idea - a new battery may cost you some money but the ability to start and use your car - priceless!
    So many lights, so little money (cause I spent it on lights). I'm not afraid of the dark, the dark is afraid of ME!

  7. #7

    Default Re: 12v. car batteries ... resting voltage ? When to replace ?

    I have found batteries last 3.5-7 years depending on how many times you forget to turn your lights off and kill the battery dead etc which can weaken it more. When your battery gets weak (assuming you have good electrical connections) your starter tends to struggle turning the motor over more especially in cold weather. The reason for doing a load test is sometimes you have a failing alternator or voltage regulator that isn't charging things well enough so voltage level isn't always the only factor in battery condition. You could also have a problem with something putting a constant drain on the battery large enough to kill it when not used for less than a week. A bad alternator diode or starter winding or some other electrical device malfunctioning (my dad had a mercury switch trunk light that came on when he parked on a hill killing the battery).
    Fenix Split rings 1400+ sent, SWIVELS now available also!
    Psalm 112:4 Light shines in the darkness for the godly. They are generous, compassionate, and righteous.

  8. #8
    Flashaholic* TooManyGizmos's Avatar
    Join Date
    Jan 2006
    Location
    Humid Florida , USA
    Posts
    3,072

    Default Re: 12v. car batteries ... resting voltage ? When to replace ?

    snip..snip...
    (my dad had a mercury switch trunk light that came on when he parked on a hill killing the battery).

    I luv that last part ....... thanks for the input .


    Also some good answers in this other thread ... after mine.
    Last edited by TooManyGizmos; 04-17-2010 at 05:56 PM.
    ~ "She" says ... ... I have ... TooManyGizmos ~

  9. #9
    Flashaholic* fivemega's Avatar
    Join Date
    Jan 2003
    Location
    California
    Posts
    3,426

    Default Re: 12v. car batteries ... resting voltage ? When to replace ?

    Measuring car battery voltage doesn't give you much usefull information unless you do it under certain load which may varry from one to other battery.
    It is important to know what kind of current (Amp) battery is capable to deliver within certain amount of time with minimum voltage of 9.6~10 volts which is enough to spin the engine fast enough in cold temperature and still enough energy for ignition system.
    Draining the battery is not as harmfull as you leave it drained for long. So if your battery is drained for any reason, immediately recharge it.
    Battery life really depends on many factors but 5 years is long enough to consider buying a new one specially in cold weather.
    Stocking with dead battery may cost you more than price of battery.

  10. #10
    Flashaholic* Wattnot's Avatar
    Join Date
    Jan 2008
    Location
    Longmont Colorado
    Posts
    947

    Default Re: 12v. car batteries ... resting voltage ? When to replace ?

    You're getting great info here but just pull into any chain auto parts store. They will test your entire electrical system with their fancy do-hicky tester and tell you if even one cell on your battery is weak. It's worth it and I have never heard about any dishonesty among them.

    Displacing night on a daily basis.

  11. #11
    Flashaholic* QtrHorse's Avatar
    Join Date
    May 2008
    Location
    Texas
    Posts
    1,159

    Default Re: 12v. car batteries ... resting voltage ? When to replace ?

    As FM stated, the battery needs to be tested under a load. There are six 2.1V cells in a 12V vehicle battery. While the vehicle is running, it should be 13.5-14.4V and while off, should be 12-12.5V.

    Cold weather will affect your batteries cranking amps more than hot weather. For instance, my batteries as of today still show to be good when I check the voltage but I know it's time to change them because we have finally started seeing some cold weather and my engine cranks over slower than when it was warmer.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •