Ask the Mechanic

Steve Thompson, Contributing Columnist

Now that October is here, and cold winter days are near, I plan to change the batteries on a couple of tractors. I've been trying to understand more about cold cranking amps (CCA) and cranking amps (CA) that are provided on the tops of batteries.

Cranking amps gets its name from the old cars and tractors that had to be started with a crank. We use these names as a power rating on how your engine will crank (with the starter in extremely cold conditions, such as Buffalo, New York) compared to usually warmer climates (such as Dallas).

Cold cranking amps is what the battery industry uses to determine a battery's ability to crank an extremely cold engine. This number measures how much current a fully charged 12-volt battery can deliver for 30 seconds (plenty of time to start a vehicle) while remaining at 7.2 volts at -18°C (-0.4°F). A battery loses voltage in a cold temperature compared to warmer temperatures. A battery at 18°C can deliver twice the power compared to the same battery at -18°C (-0.4°F).

If you live in a cold region, the CCA is something to watch. If in doubt, replace the battery with the same CCA rating as the battery in the vehicle or recommended by your servicing dealer. The cranking amps you will also see on most batteries is simply the same test given its CCA brother but done at 0°C (32°F). The CA number is usually higher than the CCA number because of the warmer test temperature.

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-- Write Steve Thompson at Ask The Mechanic, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or email mechanic@progressivefarmer.com, and be sure to include your phone number.

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