Testing Your Battery Charge

Step-by-Step Testing the Charge

Don't wait until your vehicle's dead to test your charge! With a little DieHard battery TLC, you can know your battery's life span before it kicks the bucket.
Batteries ought to be tested a few times a year, but if your busy life gets in the way of quality battery time, autumn is the best time to test. Colder temperatures require more work from your battery, so to avoid the inconvenience of a dead vehicle in the dead of winter, test the charge on your DieHard battery and be worry-free with these simple steps:

  1. Recharge your DieHard battery to 100% state of charge with the DieHard wheeled charger or the DieHard shelf charger.
  2. To avoid making a weak battery look strong, you must remove the surface charge. To do so, let your DieHard battery rest for 4 to 12 hours in a warm room before testing.
  3. If you are measuring the state of charge of a non-sealed battery, use a temperature compensating hydrometer to test the specific gravity in each of the six cells and average the findings. For sealed batteries, use a digital voltmeter to measure the open circuit voltage across the battery terminals.
  4. Use the following table and your DieHard battery's specific gravity or voltage readings to determine the state of charge.
    State of Charge Specific Gravity Voltage
    12 v 6 v
    100% 1.265 12.7 6.3
    75% 1.225 12.4 6.2
    50% 1.190 12.2 6.1
    25% 1.155 12.0 6.0
    Discharged 1.120 11.9 6.0
  5. Assess your findings. If the state of charge is 75% or lower and meets one or more of the following conditions, it's time to replace your DieHard battery:
    • There is a .050 or more difference in the specific gravity reading between the lowest and highest cells, and equalizing the battery doesn't correct the reading.
    • The battery will not recharge to a 75% or higher state of charge using the DieHard wheeled charger or DieHard shelf charger.
    • The built-in hydrometer does not read "good" after recharging.
    • The digital voltmeter reads zero volts, indicating there is an open cell in the battery.
    • The digital voltmeter reads 10.45 to 10.65 volts, indicating a shorted cell.