Batteries

Discussion in 'General Super Duty Discussion' started by dboyw, Sep 14, 2013.

Car Parts
  1. dboyw

    dboyw Full Access Member

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    After allot of checking and testing I found out the following:

    Passenger battery is good. 12.63 volts after charge, hydrometer readings almost identical across all six cells.

    Driver battery bad. 11.6 volts after charge, hydrometer five cells about the same, one cell completely dead.

    both batteries together read about 12.2 when trying to start the truck voltage drops to 8.9 truck will start, but struggles to do so.

    Batteries are three, or five years old diehard golds. Second set of diehards in the last seven years. Will not buy them again.

    What I really want to know is do I have to replace both batteries? Could I get away with just replacing the driver battery?

    I know I should, but times are tight at this time.

    Thanks for any and all help.
     
  2. DaveBen

    DaveBen SDD Senior Member

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    Yes, you must change BOTH batteries at the same time. Changing one battery will kill the new one very soon. What you really have is one battery in two places.

    Dave
     
  3. BIG JOE

    BIG JOE Full Access Member

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    What Dave said.

    Joe
     
  4. WD40

    WD40 Full Access Member

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    Yep The Masters have spoken.
    Doug
     
  5. BJS

    BJS Full Access Member

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    I'll be the one to go against sound advice... yes you're best to replace them both at the same time but depending on what your definition of money is tight is then you can replace one right now if you need it to get it going and with cooler weather coming and the reliance on glow plugs.

    if money is truly tight buy one top of the line longest warranty you can find battery today stick it in for the dead battery, it should die or be close enough that you can get a warranty swap on it and buy a new one a few years down the road or as soon as finances permit, no it's not good but it's better than a piece of yard art in the driveway.
     
  6. Y2KW57

    Y2KW57 SDD Junior Member

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    If money is tight, and the passenger battery is good, then I'd just replace the bad battery for now. A good battery will not pull down another good battery as much as a bad battery will pull down a good battery. Right now, your bad driver's battery is pulling down your good passenger battery. This status quo is a greater sin than your good passenger battery pulling down your proposed new driver's battery.

    Who's to say a "new" battery is better than a tested good battery? I've installed twin brand new good batteries in a GM truck, only to find that one of the new batteries was bad, even after testing and charging before installation. Turned out, the side post connection was intermittent inside the battery. That caused me two years of grief, cause the top posts always tested good after charging. Anyways...

    The question now, is how good is your passenger battery? 12.63 volts IMMEDIATELY after charging is not that impressive to me. A voltage reading IMMEDIATELY after charging should read about 12.9 volts. My absorbed glass mat batteries can read up to 13.4 volts immediately after charging. There is a higher surface charge that lingers immediately after charging that gives a higher reading than the voltage that battery will have the next morning when you need to start the truck.

    Try waiting a couple of hours after charging, and then take a reading. Or put a 12 volt lamp on your charged battery for a few minutes after charging, to burn off that surface charge energy, and then take a voltage reading to see what sustainable voltage your "good" battery can provide. If it is still 12.63 volts after several minutes of lamp load and a couple of hours of settling, then I'd feel comfortable getting just one battery for now. Then, when funds allow, you can pick up another new battery to match, and sell your still working passenger battery to someone else less fortunate than you.
     
  7. snicklas

    snicklas Super Moderator Staff Member

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    Another option is finances are tight...... do you have an Interstate Battery shop or distributor in your area? When I needed batteries, I went to the Interstate Battery Store and picked up a set of "blems" for less than $75 for the pair. They are just plain black batteries with no markings or stickers. They only have a 90 day warranty, but I can buy several sets at that price. I've had mine for 2 years now and are still working just fine. When I need new batteries, I will go buy another set of blems.......
     
  8. dboyw

    dboyw Full Access Member

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    Well I finally broke down and bought two motorcrafts from the dealer. They were 99.50 each, which was the best price I could find in the area.

    Thank you all for the information. I have learned quit a lot from this forum through the years, and still learning today.
     

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