How to Check an Automotive Battery Draw With the Engine Off

An automotive battery is used to start a vehicle and provides the grounding source for the vehicle chassis. Normally, an automobile's alternator generates enough power to charge the battery and supply the vehicle with power; therefore, a vehicle containing a properly operating electrical system will not require a battery replacement for several years.

There are instances, however, where a battery may become discharged, even when the vehicle is not in operation. When such a discharge happens, it is important to know how much electrical current is being drawn from the battery so that the problem may be found quickly.

Things You'll Need

• Digital ammeter with clamp probes
• Automotive battery installed in an automobile
• Slip-joint pliers
• Adjustable wrench

Instructions

1. Hold the positive battery terminal retaining bolt head with the slip-joint pliers. Loosen the nut on the battery terminal retaining bolt. Remove the positive battery terminal from the positive battery post.

2. Attach the red (positive) ammeter lead to the positive battery post. Attach the negative (black) ammeter lead to the loose battery terminal.

3. Turn on the ammeter; if the ammeter reads more than zero amperes, current is being drawn from the battery.

References

• All About Circuits: Ohm's Law - Basic Concepts and Test Equipment