A shorted or loose wire, or even a failed component in one of your vehicle's electrical circuits, may cause a drain in your battery, even when your ignition switch is off. If you find yourself with a dead battery after leaving your car in your garage overnight, it is possible that an electrical leak is discharging your battery. You may check battery drainage in a few minutes using a few tools at home. This will save you time in finding the problem and help extend the life of your battery.
Open the hood of your vehicle and remove the under hood light bulb.
Remove the fuse for the dash clock from the fuse box under the instrument panel or dashboard using a fuse puller, if your car has dash clock installed.
Remove the ignition key, make sure all the accessories are off and close all the vehicle doors and trunk.
Detach the negative (black) battery cable using a wrench and clean the battery post and cable terminal, if necessary, using a battery-post cleaning tool.
Get your digital multimeter and set the meter to direct current (DC) so that you may read above 10mA.
Connect the negative (black) probe on your meter to the negative battery post and the red probe on your meter to the cable terminal you disconnected in Step 4.
Turn on your meter. Your meter readout should be between zero and 10mA. Otherwise, you have just detected a drain on your battery.
Ask an assistant to get behind the wheel of your car and close the door, if you have detected a current drain on your battery. Tell your assistant to start pulling and replacing fuses from the fuse box, one at a time, until the current displayed on your meter drops bellow 10mA or close to zero. A drop in the meter reading upon removal of a fuse will indicate the component or circuit causing the drain.
Inspect, troubleshoot or take your vehicle to an automotive electrical repair shop to find the cause of the current drain.
Replace the fuse for the dash clock, the under hood light bulb, and the negative (black) battery cable using the wrench.
