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Questions and Answers

Battery State Of Charge Testing

Q. Hey Vincent, I need to get hold of a battery tester that will measure or indicate whether there are still some juice in a battery. Measuring the voltage is easy with a multi-tester or voltmeter. But how do measure the amount of current stored in car battery after charging it? It will show a 12 volt charge but the battery will not start the engine.

Battery State Of Charge Testing

Can you please tell the name of this instrument, is it the load tester? And where can I get one of this?

Thanks again, you've been a great help.

A. What you need to get is a battery hydrometer. This will measure the state of battery charge. You can get them just about anywhere, parts stores, Wal-Mart, Sears, etc.

I would recommend the float type hydrometer, like the Blue Point Battery Hydrometer, versus the floating ball type. The float type is much easier to read. In general, here is how to check the battery state of charge. Anything above 12.50 is considered good.

Battery State Of Charge Testing
  1. If the battery has been charged within the last four hours, remove the Surface Charge. If the battery has been discharged within the last 15 minutes, wait for at least 15 minutes before testing it.
  2. While holding a clean hydrometer vertically and wearing glasses, squeeze the rubber bulb, insert the nozzle into the electrolyte in the cell, and release the bulb. The electrolyte will be sucked up into the barrel or container allowing the float to ride freely. Start with the cell that is closest to the POSITIVE (+) terminal.
  3. Squeeze the rubber bulb to release the electrolyte back into the battery's cell.
  4. To increase the accuracy of the measurement, in the same cell, repeat this process several times so the float will reach the same temperature as the electrolyte.
  1. At eye level and with the float steady, read the Specific Gravity at the point the surface of the electrolyte crosses the float markings. The Specific Gravity reading should be between 12.50 and 13.00.
  2. Release the electrolyte back into the cell from which it was taken and record the reading. Be sure to avoid spillage.
  3. Repeat the process for each individual cell. The Specific Gravity reading should not have a difference of more that 25 "points" between the lowest and highest reading with the battery fully charged. If so, try and equalize the battery by following the battery manufacturer's procedures. If equalizing does not help, replace the battery.
  4. Thoroughly rinse the hydrometer with water after using it.

Additional Information provided courtesy of AllDATA

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