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OT: 80's pickup Battery, Alternator, or ?

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  • OT: 80's pickup Battery, Alternator, or ?

    I have a 1984 Chevy pickup (carbureted) that I plow the yard with in the winter and it sits and rots the rest of the year. Lately it has to be jump started because the battery doesn't have what it takes (click click click).

    The battery is an 1100 CCA Duralast Gold from Autozone, maybe 5 years or older (my memory sucks). It's been neglected by my forgetfulness to maintain it during the summer months. The alternator is a re-manufacture from Autozone that I installed maybe 5-7? years ago. The truck probably runs about 20 hours a year.

    After the truck sat unused for 5 days the battery measured 11.9v. I jumped it and with the truck running it measures 15v. With the truck running and battery disconnected the leads that would hook to the battery measure 15.8v. I'm trying to determine if there is a battery or alternator problem.

    EDIT: The 15v+ measurements were while the motor idling but cold, so RPM's were higher than a normal warm idle.

    I don't mind replacing the battery and/or alternator but would appreciate opinions on the matter. I don't want to put in a new battery if the alternator is going to assassinate it. 15v sounds high to me, what says you? Thanks.
    Last edited by SirLesPatterson; 12-30-2017, 12:59 PM.

  • #2
    While charging the voltage at the battery should be between 14.2 and 14.6. At 15.8 volts your alternator is cooking the battery which leads to short battery life.


    • #3
      It should charge at 14.8 V (max) but the difference you see could very well be just your voltmeter reading a shade high.
      Location: Saskatoon, Saskatchewan, Canada


      • #4
        If I understand you correctly, you have 15v at fast idle which is good. So the charging system was is ok. Batteries in reality only have a 4 to 6 year life span (but often work longer). Infrequent use will shorten the battery life. Very cold & hot weather is also hard on battery life. Replacing it would not be be a bad idea at all. I had this same problem recently with my wife's car who uses it infrequently and was very old but we keep it in a heated garage so that helped extend its life.
        For a replacement, I would suggest you put in a high end, high cranking amp hour replacement. In other words not a cheapee because you want the long cranking power due to infrequent use. A cheaper battery is cheap because it doesn't have that. Hope this helps!


        • #5
          Your use is the worst possible scenario for battery longevity when they are not kept up to proper voltage.
          Newer batteries just do not hold up to many discharge/charge cycles.
          You can try a low amperage trickle charger for starters, it may bring it back to a useful life, then keep it on a maintaining charge when not in use. 15v initially is not a problem but it is high if it stays there and does not drop as the battery charges, does not sound like a bad alternator to me though.


          • #6
            As mentioned, never disconnect the alternator while the engine is running, you just dodged a bullet.
            Regulators are temperature compensated. They are programed to put out a higher voltage when cold and also to decrease that voltage when warm so as not to cook the battery. Measure it on a hot day and it should be around 14.2-14.5 volts
            The battery is toast.
            Home, down in the valley behind the Red Angus
            Bad Decisions Make Good Stories​

            Location: British Columbia


            • #7
              Originally posted by RMinMN View Post
              While charging the voltage at the battery should be between 14.2 and 14.6. At 15.8 volts your alternator is cooking the battery which leads to short battery life.
              Later model GM alternators put out ~15 volts. The OP says his is a reman (which probably fits dozens of different years/models) so it's actually not off-spec. It does lead to shorter battery and headlight life.


              • #8
                Alternator regulators are temp compensated to raise the output voltage in cold weather to properly charge the battery. Lead acid batteries simply require more voltage in cold weather to get fully charged. My 99 Silverado's voltmeter definitely shows higher on a cold morning and will drop back as the engine compartment warms up. In the absence off additional data, I think your alternator is OK. Your battery is not OK. See https://autoelectricalsystems.wordpr...-compensation/

                Last edited by RWO; 12-30-2017, 01:44 PM.


                • #9
                  Thanks for your input everyone. Since my initial post have let the truck warm up it measures 14.7 at battery so I agree with you all that the alternator is likely okay. Also funny thing since someone mentioned it... I did use two voltmeters to confirm readings since my digital one said it had a low battery I confirmed with my old analog one. I also found my old carbon pile load tester and the battery failed miserably. I now have it out of the vehicle and hooked to a charger after which I will test it one more time but ultimately I think it's simply time for a new battery. Thanks again!


                  • #10
                    NEW battery time.

                    You let a battery sit 2 months, and it will be damaged. Let it sit 6 or more, and do that a couple times, and it is REALLY damaged. Sulfated up and low capacity now.

                    It takes only about 2 or 3 ampere hours capacity to start a vehicle, but your letting it sit has drawn you down probably below that. Never let the battery sit. Even with older vehicles that do NOT put a constant load on.

                    Get one of those solar maintainers, and clip it on for your new battery. They work very well.
                    1601 2137 5683 1002 1437

                    Keep eye on ball.
                    Hashim Khan

                    If you look closely at a digital signal, you find out it is really analog......


                    • #11
                      So, funny thing related to all this. I recently replaced my old roll around battery charger/jump starter because I thought it defective since it wouldn't charge this battery and it's output measured 10v in 2A trickle charge mode with no load. (Also I had run over it with a truck very recently) Anyhow it ends up that this battery was bad and my brand new charger measures 8.5v in 2A mode with no load attached and a friends charger measures 10v so I guess that's normal, something to do with them not being true DC output. Long story short now I have 2 chargers, which is not a bad thing. I just now took some time to massage the sheet metal of the old charger back into shape enough to reassemble it. Man it looks like it's been to hell and back but it lives to charge another day!


                      • #12
                        Originally posted by RMinMN View Post
                        While charging the voltage at the battery should be between 14.2 and 14.6. At 15.8 volts your alternator is cooking the battery which leads to short battery life.
                        If the battery has perished and has a really high internal resistance it's not unlikely that the voltage will rise to something like that 15.8. I've seen that happen on dead batteries and also on the old non sealed filler cap style wet cells that were allowed to go dry. So I wouldn't blame the charging system just yet.

                        5 years out of a battery that is neglected like this one has been is frankly darn amazing.

                        If you want to keep on using the truck in this way I'd suggest you don't put a battery into it at all other than for during the winter. Instead consider the idea of one of the crazy super capacitors that you use to start and run the truck. They aren't much more costly than a battery. And you should be able to let them sit all summer and then put them in the truck and charge it up with a battery charger. You may want to jump it the first time around off another battery if it is hard starting. But if it generally fires right up than the capacitor should handle it.

                        Warning though. You'll want to find out if the super caps are OK with sitting idle and what their storage condition should be. You MAY need to keep some minimal charge on them. Do some research first.
                        Last edited by BCRider; 12-30-2017, 07:15 PM.
                        Chilliwack BC, Canada


                        • #13
                          If you disconnected the battery and the engine kept running,then the alternator was functioning assuming a gas engine with a distributor.

                          Simple check to see if an older model alternator is charging without disconnecting anything.Touch a screwdriver to the rear bearing cap on the back of the alternator while the engine is running.If the alternator is exciting the armature the cap will be magnetized and the scredriver will stick to it.Odds are if the armature is being excited the alternator is functioning.

                          One of these is also handy-
                          I just need one more tool,just one!


                          • #14
                            It looks like the charge voltage limit is 2.5 volts/cell at 0C (32F), which is 15V for a 12V battery:

                            Paul , P S Technology, Inc. and MrTibbs
                            USA Maryland 21030


                            • #15
                              Before starting the vehicle in the morning pop the hood and feel the alternator to see if it is warm at all.

                              Start the truck and disconnect the battery while it is running.

                              Last check voltage at the battery (hooked up now) with the truck running. Should be around 13.9-14.5v running.

                              If the alternator is warm to the touch in the morning it is draining the battery and should be replaced.

                              If the truck dies when the battery is disconnected the alternator is bad.

                              If the volt meter shows anything in the low 12's-11's while running the alternator is bad.

                              If all else checks out the battery is bad.

                              This all given the alternator has an internal regulator.