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HiTech's avatar
HiTech
Explorer
May 23, 2013

Checking hydrometer accuracy with charged battery voltage

Is it true that:

Specific Gravity = Cell Open Circuit Voltage - 0.845?

Could one average the specific gravity readings across cells in a battery, and use this formula to check the accuracy of the voltmeter and/or hydrometer (based on which one is calibrated better)?

Jim

22 Replies

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  • HiTech's avatar
    HiTech
    Explorer
    May 24, 2013
    Is that too high? My AGMs do 12.94 after 24 hours and my always float charged flooded Duralast gets up over 12.8 after a 24 hour rest. I wonder where yours would stabilize out at.

    Jim
  • BFL13's avatar
    BFL13
    Explorer II
    May 24, 2013
    Baseline SG on my Interstate 6s is 1.300 When I get that they still have a surface charge from just having been "overcharged" so no idea of their "resting voltage" at that point. Then they go on Float so I never see their "resting voltage" anyway

    1.300 + 0.845 = 2.145 x 6 = 12.87v so that is too high for their resting voltage I think.

    This indicates your notion ASSumes a standard acidity for batteries, when we know they vary by brand and for what ambient temp intended service?

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