Coated battery terminals do not necessarily guarantee good electrical connections. A voltage drop test, not a visual inspection, is the only way to verify that any connection is electrically sound. There are several ways to reduce battery terminal corrosion, including coating the outside of the connection with a thick layer of petroleum jelly or chassis or wheel-bearing grease, or spraying the outside of the terminals with a corrosion-resistant chemical.
However, treating the outside of the battery terminal won't prevent salt and moisture from penetrating the tiny air gaps between the battery post or side terminal and the battery cable terminal.
The most common symptom of corroded battery terminals is a no-start problem or a sluggish starter motor. Ignore outward appearances and use a digital voltmeter to measure the voltage loss between the battery terminals and battery cable terminals. If the voltmeter lacks an auto-ranging capability, select the lowest voltage scale for this test.
After disabling the ignition system or electric fuel pump, press the tip of one voltmeter probe firmly against the top of the battery post and hold the other probe against the cable terminal. Or clip the other test lead onto the cable terminal. Crank the engine for about 10 seconds. If the voltmeter reading exceeds about 0.10 volt, clean the connection and retest.
To test a side-terminal battery connection, clip one voltmeter lead onto the head of the side-terminal bolt. Use a sharp, wire-piercing voltmeter test probe to pierce the battery cable about an inch from the cable terminal, then crank the engine and look for a voltage reading of about 0.10 volt or less.
After cleaning the cable, seal the pierced insulation with heat-shrinkable wrapping or tubing.
To skip the cable-piercing step, connect the voltmeter between the starter and battery terminals. If voltage exceeds about 0.20 volt when you crank the engine, check for a corroded battery terminal first. If the connection's corroded, clean it and retest. If the terminal is clean, replace the cable.
Starting and charging system diagnosis was the subject of the Parts & Labor section published in the May 16 issue of TIRE BUSINESS.