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  • diesel batteries

    A guy I know has a '08 diesel Ram. He thinks his alternator is shot. Both batteries are reading 11.7v and of course won't start. If he gets it started, will it run off the batteries, or can he drive it and just not shut it off...... I have my thoughts...

    Thanks...

  • #2
    Old school diesels didn't need a battery once running. If it's controlled by a computer now, it will need fully charged, good batteries if the alternator in not working. It will only run till the batteries won't supply enough voltage/ amps to run the computer.
    If ya can't fix it with a hammer,ya got yourself an electrical problem.

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    • #3
      That was my thought. I'm guessing an '08 is new school? I'm thinking that goes w/o saying...

      Thanks Grub

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      • #4
        12 volts is fully discharged, 11.7 volts is a dead battery. 13.4 volts is a freshly charged battery
        Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

        1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

        Past Boats
        1970 Wooster Hellion - Merc 9.8
        2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
        1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

        What’s behind you doesn’t matter.Enzo Ferrari

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        • #5
          This was going on with my 08 last year and nephew's 07 the year before. The truck as one shorted cell battery. Disconnect one of the bats and measure each. Replaced my bats with Duracell at Sams
          94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
          95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
          07 Seadoo GTX
          Merc Adults Only VP Adults Only
          G-Dad always said "First Liar doesn't stand a chance"

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          • #6
            Originally posted by Scott Danforth View Post
            12 volts is fully discharged, 11.7 volts is a dead battery. 13.4 volts is a freshly charged battery
            That always amazed me that it doesn't take much of a voltage drop to not turnover the engine...

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            • #7
              Originally posted by AllDodge View Post
              This was going on with my 08 last year and nephew's 07 the year before. The truck as one shorted cell battery. Disconnect one of the bats and measure each. Replaced my bats with Duracell at Sams
              I sent the guy the info. He already has a guy coming up from his hometown with a trailer, 3hrs away.. If I would have known earlier we could have checked the output of the alt and determined if was the bats or the alt. Owell...

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              • #8
                An '08 needs fully charged batteries to run, it is amazing how little it takes in voltage/amp drop will kill them.

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                • #9
                  He charged the bats. One was over 13v, the other 12 something. Could be a bad one. Its on a trailer heading south...

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                  • #10
                    It will run fine with just one bat, so long as the Pos doesn't contact ground
                    94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
                    95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
                    07 Seadoo GTX
                    Merc Adults Only VP Adults Only
                    G-Dad always said "First Liar doesn't stand a chance"

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                    • #11
                      Seems the good bat wasnt the primary. It was on the drivers side. I believe the primary is the passenger side.

                      I know nothing about diesels except I would like a newer dually...

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                      • #12
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                        There is no primary or secondary, they are both in parallel (12V and more amps). Only time they could use 2 bats is on real cold days using the grid heater to warm the air before cranking
                        94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
                        95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
                        07 Seadoo GTX
                        Merc Adults Only VP Adults Only
                        G-Dad always said "First Liar doesn't stand a chance"

                        Comment

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