What is a good 12V battery voltage reading?

Electrical & Ignition

  1. Kern Dog

    Kern Dog FBBO Gold Member FBBO Gold Member

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    I have used traditional Lead/acid batteries in all of my cars except the Charger. The lead/acid batteries seem to all test over 12.5 volts in the cars I have here. The Charger had a Red Top Optima until recently. It lost charge frequently and charging it was always a pisser since the gel-cell design had a unique charging procedure. ( I do not have a specific gel cell charger) Even when charged to the point where the charging unit shut off, it never got over 12.3 volts.
    Many times it read under 12. It has lost charge a few times lately so I decided to replace it. I had planned to get a regular lead/acid battery but the guy at NAPA convinced me that the AGM one he had would last longer as long as I put a slow trickle charge on it when I expect the car to sit awhile.
    The one I bought tested at 12.6 even after sitting on a shelf awhile. I also bought a small trickle type charging unit.
    At home, I charged a battery from my 67 Dart. Today it tested at 13.06 volts! What? I don't recall ever seeing any of my batteries test over 13 volts before! I put the charging unit on the new battery to see where it ends up.
    I have used Optima batteries in my '70 Charger since 2002. The starter never spun real fast but it was always enough to start the car.
    I can't start the car now yet though. I have the carburetor at a friends shop. I'm anxious though to see how it spins over with a better battery.
     
  2. dadsbee

    dadsbee FBBO Gold Member FBBO Gold Member

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    DO NOT trickle charge an AGM. Kill it partially if need be and then hit it pretty hard with 14+ volts to charge at about 8 amps. No need to maintenance charge a good AGM.

    Ford telling me that my 2 year old battery in my F150 is good today.. even though within 2 days of charging my auto stop/start won't work because the truck knows it's charging the battery. Tech put it in their fangled tester and it showed 12.23 volts and drew only 379 CCA on it's 760 CCA rating. Charged it and then it tested fine.. even though I've done this twice myself they wouldn't give me a new battery. I booked an appointment for next Friday so they could do it again... lol I have prepaid maintenance and these f'rs are going to learn a lesson or three.

    A freshly charged battery should read in the 13.2 / 13.6 range. A good one sitting for a bit at least 12.6
     
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    • Johnpat

      Johnpat Well-Known Member

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      My understanding is from 12.7 - 13.5 depending
      on how long it sits after being charged.
       
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      • Kern Dog

        Kern Dog FBBO Gold Member FBBO Gold Member

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        I have no way to control the charge rate or the amperage. I have a big Schumacher charger/start assist unit on wheels and the small 2V unit.
         
      • dadsbee

        dadsbee FBBO Gold Member FBBO Gold Member

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        Use the big one about 10 minutes at a time. Feel the case and if it's getting warm shut it off and let cool, repeat until you're happy it should be charged. DO NOT leave it hooked up and unattended.. IE forget you hooked it up.. don't ask! LOL
         
      • RJRENTON

        RJRENTON FBBO Gold Member FBBO Gold Member

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        You state that "do not trickle charge an AGM bsttery". WHY? Who made this determination.....the battery manufacturer? But to partially discharge it (to what level and is it a percentage of the total capacity in terms of CCA, CA or amp-hour x hours)? How is this accomplished?
        The level of the battery's charge USED to be based on the Specific Gravity of the electrolyte, corrected for temperature. The range for a fully charged battery was 1,260 - 1.270 as measured with hydrometer. As the charge decreased, the Specific Gravity of the electrolyte would decrease. Conversely, charging the battery will increase the Specific Gravity of the electrolyte. The old Delco "Magic Eye" energizer, the hydrometer was the eye, and as long as it was green, the battery's charge was OK.. A 12 volt lead acid battery produces 12 volts or 2 volts per cell x 6 cells ir 12 volts. The residual surface change will usually be about 12.5 - 13.0 volts. Typical automotive charging system produce 14.5 volts nominal to overcome the battery's internal resistance and drive the lead acid chemical reaction to increase the Specific Gravity of the electrolyte.
        With the advent of the sealed maintenance free battery, checking specific gravity is not possible. The battery must be load tested and the terminal voltage checked while under load to get an idea of the battery's capabilities. The manufacturer will provide these testing ranges for his product. The advantage of the spiral wound gelled elrctrolyte construction is lower internal resistance which will yield higher cranking amperage but it requires specific testing procedures. Don't guess but inquire of the manufacturer. Just my opinion of course.
        BOB RENTON
         
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        • dadsbee

          dadsbee FBBO Gold Member FBBO Gold Member

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          You know Bob, I had a Maintenance Supervisor that questioned everything I did as the plant Engineer back in the '80's while working in the most modern glass bottle plant in North America and he did all he could to discredit my knowledge because I was 20 years his junior .... and when it came down to it he had no idea what his job really was. From this and other previous posts of yours at me it seems you're on the same track for some reason and as I told him, do your own research and maybe you'll keep YOUR job. You type a lot of redirect and never seem to offer any real advise here.
           
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          • cryplydog

            cryplydog FBBO Gold Member FBBO Gold Member

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            The way it is supposed to work in a perfect world is 2.2 volts per cell and 13.2 total.
             
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            • mopar 3 B

              mopar 3 B Well-Known Member

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              Given the number of vehicles produced since 2000 by GM that will not start with less than 12.8V how can it be that a new battery with less voltage would be acceptable?
               
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              • dadsbee

                dadsbee FBBO Gold Member FBBO Gold Member

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                Even my 2007 Mercury Verado on my boat won't attempt a start below 11.7 volts, tempting fate to boost it if it says "no" as well.
                 
              • Kern Dog

                Kern Dog FBBO Gold Member FBBO Gold Member

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                That is unusual. Under 12.8 and it won't start a new GM car ???
                 
              • mopar 3 B

                mopar 3 B Well-Known Member

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                Nothing unusual. A bit stupid. Son in-laws 1999 Grandam would not start at 12.5v. The headlights would only stay on for a short time before system management put them out. Grandsons 04 is the same way.
                 
              • Kern Dog

                Kern Dog FBBO Gold Member FBBO Gold Member

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                It is unusual to me.
                 
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                • Beekeeper

                  Beekeeper Well-Known Member

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                  We maintain DC battery banks on a daily bases and DC cells put out 2.2 volts
                   
                • Kern Dog

                  Kern Dog FBBO Gold Member FBBO Gold Member

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                  This is interesting. I have rarely seen any of my batteries over 13 volts. I just charged the new AGM for 2 hours and it came up from 12.6 to 13.2.
                   
                • Frank Mopar

                  Frank Mopar Well-Known Member

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                  Interesting dadsbee. So what did the dealer say is the reason the autostart did not work?
                   
                • Ranger16

                  Ranger16 Well-Known Member

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                  Now I'M confused. I always thought a fully charged battery was 12.6v (2.1v per cell).

                  battery voltage.jpg
                   
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                  • dadsbee

                    dadsbee FBBO Gold Member FBBO Gold Member

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                    It doesn't work because the computer knows it's charging the battery and shouldn't shut off. Nothing wrong with the A/S system. So their Ford service protocol is they have to charge the battery and then of course the auto start works again.. for about 2 days (I'd already done this myself twice before taking the truck in)! Once the battery is charged they can't get a "fail" on their fancy battery charger/tester so Ford won't let the dealer install a new battery on the prepaid maintenance plan.

                    I'm certain it will get a new battery next Friday, as I picked my truck up last night and of all things on my 6 month cycle prepaid maintenance they did everything they were supposed to EXCEPT they forgot to do my oil change, let alone add the missing quart of oil while I'm in the middle of oil usage monitoring to get a new engine in my '18 F150. Had to have the Service Manager go out and put a quart in the truck before I left the dealership and he was looking for a head to cut off when I left, after stating " I guess I'll order you an engine in about a month" and I added and a battery for next Friday.
                     
                  • Beekeeper

                    Beekeeper Well-Known Member

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                  • Dennis H

                    Dennis H FBBO Gold Member FBBO Gold Member

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                    C1095985-4F1D-443F-A745-04CD94C63DBA.png Jesus Chrysler. Wish the agm debate would settle. 09 Challenger-original battery.
                    No agm application for the 69.
                     
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