Battery Service

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PARASITIC DRAIN Check for excessive battery drain or parasitic loads using an ammeter. Make sure all electrical loads are off in the car, doors closed, and the key is out of the ignition switch . Disconnect one of the battery cables from the battery, placing an ammeter in series between the battery post and cable clamp. The current draw reading should be less than 35 milliamps. A reading higher than this (or manufacturer specifications) would indicate excessive battery drain. Something is "on", allowing current to flow running down the battery. Vehicles today typically will draw less than .020 amps (20 milliamps) of current to maintain electronic memories and circuits.

Note: If the battery is disconnected parasitic drains may temporarily increase. Circuits in the engine and body computers are activated and will run until internal timers runout. This reactivation period could be anywhere from a few seconds to almost 30 minutes. Whenever possible avoid disconnecting the battery while performing this test. It is possible to place one lead of the ammeter on the battery post and the other on the battery clamp, while at the same time lifting the battery clamp off the battery post. On side terminal batteries, connect the voltmeter with alligator clips and let sit until the timers run out.