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Knowledge Base : Frequently Asked Questions : Powersports Batteries FAQ : Why is My 12 Volt Battery Reading as 13 Volts?

Why is My 12 Volt Battery Reading as 13 Volts?

Inside diagram of Lead acid battery

All Lead acid batteries (Gel, AGM, Flooded, Drycell, etc) are made up of a series of 2.2 volt cells that are bridged together in series to reach their final desired voltage. For instance, a 6 volt battery will have 3 cells (3 x2.2= 6.6 volts), a 12 volt battery will have 6 cells (6 x2.2=13.2 volts) and so on.That 2.2 volts is the fully charged, straight off the charger number. The actual resting voltage, or the voltage a battery will settle at 12-24 hours after being removed from the charger, is closer to 2.1 volts per cell, or about 6.4 volts for a 6v battery, and 12.7 volts for a 12v battery. These numbers assume 100% healthy cells, and may vary a bit lower for older batteries.


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  • Very helpful information and well-written for a non-technical college grad. Thank you

    Joan
    April 23, 2012 a 9:02 am
    • I have 6 8volt batteries that are dead. My charger won‘t charge them because they are below 20 %. and they are 5 years old. Can they be saved?

      Tim
      January 21, 2013 a 11:22 am
      • If the 8 volt charger won‘t do it, try using a 6 volt charger to bring them up to the point where the 8 volt charger can ‘read them’ and turn on.

        BatteryStuff Tech
        January 21, 2013 a 12:20 pm
      • Excellent article. Thank you. The motorcraft XBT66-650 has a date code of Dec. 2007. This is by far the longest lasting battery we’ve ever had. The day following a cold snap it wouldn’t start. I charged it & its lasted another 2 mths. Then again last nite, it wouldn’t start the car. It read 11.86. I charged it, it now reads 12.54. And starts fine. The prorated warranty is for 100 mths. I’m surprised it lasted 84 mths. I will be getting another one. The cenntenials lasted 4 1/2 years, like clockwork. The Bosch batteries lasted 2 1/2 years like clockwork. For $20 more I will stick with the motorcraft

        Dd
        November 23, 2014 a 12:33 pm
        • I have had good luck with Motorcraft. The one in my old 91 Sable lasted 7 or 8 years. The ones in a 99 diesel Ford have been there since I got it. And that was in 2008, 8 years ago. Had a few close calls where I thought they would be changed… so far so good. I think the date code is 2004 or 05.

          JJ
          June 11, 2016 a 12:18 pm
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