Car Doctor Q&A: Side Terminal Batteries and Corrosion

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The location of battery terminals can often exacerbate corrosion problems that can cause slow cranking issues. AAA Car Doctor John Paul explains how to test to find hidden corrosion issues.

Q. I have a 2007 Isuzu Ascender (yes I was one of the few that purchased one) and I’m have a problem with the car not starting. It acts like it has a dead battery.

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I did replace the battery but it still from time to time cranks over very slow or clicks. Other times it starts just fine. Because this is an Isuzu not many people even want to look at it. Any thoughts?

A. I’m surprised that you are having trouble getting someone to work on your Isuzu, it really is just a GMC Envoy with Isuzu badging.

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One very common issue with these side terminal batteries is that corrosion builds up and causes a poor connection.

The best test for this is called voltage drop. In this test you are looking for “lost” voltage from the battery to the starter and from the battery to ground (or whatever component you are testing).

Western Wyoming Community College produced a great video showing the procedure:

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Ideally there will be little or no voltage drop across a connection, switch or wire. As a general rule with voltage drop you don’t want to see more than .5 volts on the power side and .1 of a volt on the ground side.

Start with disconnecting the battery and measure the voltage. Then reconnect the battery cable and measure the voltage again. Too often the issue is right at these side terminal connections that build up with corrosion.

Due to the makeup of the connector this can be hard to spot. Start measuring voltage at junction points to the starter and grounds. Having a helper that can crank the engine while you are measuring voltage is helpful. All of these tests can be performed with a simple digital multi meter.

John Paul is public affairs manager for AAA Southern New England. A certified mechanic, Paul tests dozens of new cars each year and also hosts a radio show on AM 950 and 550.