How do I test for a parasitic battery draw?

Turn everything off (no lights, no doors open, key off), disconnect the battery (-) cable, and attach an amp meter set to the milliamp scale between the clamp and the battery post. Temporarily install a 12 gauge wire between the battery (-) cable and battery (-) post, turn the key on for 10 seconds without starting the engine, then turn the key off, close the door, and remove the temporary wire before reading the meter.

What is an acceptable parasitic draw reading?

The meter should not read more than 50 mA, or about 0.05 amps.

How do I find which circuit is causing the battery drain?

If the reading is higher than 50 mA, remove fuses one by one. As soon as the reading drops below 50 mA, you have located the circuit causing the draw.

When is the unwanted draw test needed?

This test is only required if the battery keeps running down after sitting for a day or two.

Should the engine be started during the test?

No. Turn the key to the on position for 10 seconds but do not start the engine.

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Parasitic Battery Draw Test Procedure - Checking for Unwanted Draw (Wilson)

Alternator parasitic draw test instructions with battery, ammeter and fuse box diagram

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Step-by-step procedure for checking unwanted parasitic draw at the alternator using an ammeter and fuse box.

AI caption August 2018 · Photo 223 of 224

This is a page from a Wilson Electrical Products reference titled "Testing the Alternator," specifically covering the procedure "Checking for Unwanted Draw" (parasitic battery drain). The test applies when a vehicle's battery keeps running down after sitting for a day or two. The procedure instructs the reader to turn everything off (no lights, no doors open, key off), disconnect the negative battery cable, and connect an ammeter set to the milliamp scale between the cable clamp and the battery post. A temporary 12-gauge jumper wire is installed between the negative cable and negative post while the key is turned to the on position for 10 seconds (without starting the engine). After turning the key off, closing the door, and removing the temporary wire, the meter should show a milliamp reading no greater than 50 mA (about 0.05 amps). If the reading is higher, the document explains how to isolate the offending circuit by pulling fuses one at a time until the reading drops below 50 mA. Illustrations show a battery, digital multimeter, negative cable clamp, and a hand removing a fuse from a fuse box. The page is generic to any 12-volt automotive electrical system and is not vehicle-specific.

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Frequently asked questions

How do I test for a parasitic battery draw?: Turn everything off (no lights, no doors open, key off), disconnect the battery (-) cable, and attach an amp meter set to the milliamp scale between the clamp and the battery post. Temporarily install a 12 gauge wire between the battery (-) cable and battery (-) post, turn the key on for 10 seconds without starting the engine, then turn the key off, close the door, and remove the temporary wire before reading the meter.
What is an acceptable parasitic draw reading?: The meter should not read more than 50 mA, or about 0.05 amps.
How do I find which circuit is causing the battery drain?: If the reading is higher than 50 mA, remove fuses one by one. As soon as the reading drops below 50 mA, you have located the circuit causing the draw.
When is the unwanted draw test needed?: This test is only required if the battery keeps running down after sitting for a day or two.
Should the engine be started during the test?: No. Turn the key to the on position for 10 seconds but do not start the engine.