How To Check for Draw on Battery: Troubleshooting Steps

We will look at how to check for a draw on battery if there’s a fault below.

Battery draw refers to electrical devices pulling energy from this power source, slowly draining the battery charge.

No component should draw energy from the battery when the vehicle is off unless it is the alarm system or other security features.

And these systems consume little energy when on standby.

If parasitic draws exist, they can kill the battery, leaving no power to start. If you experience this issue, you can check for high energy draws in your battery using these steps.

Battery Draw/Drain Troubleshooting Steps
Parasitic Battery Drain Causes
Automotive Battery Failure/Battery Drain Signs
Wrap Up

Battery Draw/Drain Troubleshooting Steps

You will need the following tools to check this issue.

OBD II scanner
Test light
Multimeter
Socket or open-end wrench
Tiny clamps or zip ties
Fuse puller
Protective gloves

Step 1: Scan for Trouble Codes

Before you get deep into the electrical system to locate the issue, scan the vehicle’s diagnostics using an OBD II scanner.

The faulty component draining power from the battery might have thrown an error code, making it easier to spot the culprit.

Step 2: Check the Alternator

If there are no error codes, test the alternator using a multimeter when the engine is on.

A faulty unit might not generate enough electricity to run the vehicle’s electrical systems and recharge the battery.

Alternators should output about 13.5 to 14.5V, and their current output should match the rating printed on it.

These can vary from 60 to 150 amps in modern vehicles.

A car alternator

So set the multimeter to 20V DC, then check the voltage rating.

First, turn off the vehicle and connect the red multimeter probe on the battery’s positive terminal and the black probe on the negative terminal.

The reading should be about 12V.

Start the vehicle, then connect the multimeter to the battery terminals like above. If the reading is about 13.5-15V, the alternator is healthy.

Step 3: Check if the Battery Has a Drain

Parasitic draws are not always apparent. So you might only notice things like extended low-power cranking when starting the engine after parking it for a long time.

Therefore, if there are no error codes and the alternator is okay, it’s time to get deep into the electrical system, beginning with the battery.

A mechanic replacing a car battery

The easiest way to conduct parasitic draw tests on the battery is using a test light. First, connect this test light to the car battery terminals to check if it lights up. If not, get another test light and re-test it.

Step 4: Turn Off All Electrical Components in the Vehicle

Power off all your vehicle’s electrical devices, which include headlights, cabin lights, head units, etc.

Turning off the engine and ignition switch turns off most of these components. Also, lower the power windows, then close the doors to prevent accidental electrical shorts.

Step 5: Disconnect the Negative Battery Cable

Some vehicles have their battery in the hood and others in the trunk.

Locate the battery first, then disconnect the negative cable, which should have a black cover or insulation.

Loosen the negative terminal using the wrench, and use the correct wrench size to loosen the bolt to avoid wearing the sides.

A mechanic loosening the negative battery lug using a wrench

Most of these bolts are size 10. If unsure about the size, use an adjustable wrench. Loosen this bolt until the lug comes off the terminal post without applying pressure.

Step 6: Test for Parasitic Battery Drain

A test light has two terminals. Connect one end to the negative battery post and the other to the negative battery cable you removed in the previous step.

This connection completes the circuit to the power source.

So if there is no parasitic power draw, electric current will not flow from the positive to the negative battery post, meaning the test light will not glow.

But if there’s a parasitic drain, the light will illuminate. If the latter occurs, proceed to step 7.

The alternative is to replace the test light with a millimeter in the same position, which will measure the amperage reading between the terminal and the wire.

Remember to set it to the correct amperage settings in the DC zone (10 amps at most).

A technician using a multimeter to measure a car battery’s voltage

Step 7: Locate the Fuse Box

If you’ve established there is an electric current drain, troubleshoot the issue from the fuse box.

All vehicle electrical components draw power from the battery via a fuse in the box for circuit protection.

So this box provides a central location for identifying electrical faults in the vehicle.

An electrician using a multimeter to test fuse voltages in a fuse box

Find this component, then unlock and remove its cover. After that, position the test light or multimeter to be easily visible from where you are on the fuse box.

Step 8: Disconnect and Reconnect the Fuses

Use the fuse puller to remove the fuses one after the other while checking the test light or multimeter reading.

A multimeter is more accurate because it will show the amperage for even the slightest drain. Monitoring the light illumination can be tricky.

You must be super keen.

After removing the fuse and checking the multimeter, insert each fuse back into its slot before proceeding to the next one.

If you pull a fuse and the amperage reading drops to zero, that is the culprit.

An auto mechanic using a fuse puller to pull fuses from the fuse box

The problem might be the fuse or the component connected via that fuse.

So install another fuse with a similar power rating in that slot. If the reading is zero, the issue is the fuse. Replace it, and that’s it.

But if you get a reading, the electrical draw issue is probably in the connected component.

Locate this component and its wiring to troubleshoot the problem.

Once you’ve solved the issue, reassemble the fuse box, disconnect the millimeter or test light, then reattach the negative battery cable to the negative terminal.

Parasitic Battery Drain Causes

Cars pull some power when off, and the standard battery drain when you turn off the ignition switch and lock the car is less than 50 milliamps in old vehicles.

Newer cars pull about 50 to 85 milliamps. Devices causing this current draw include things like internal clocks and alarm systems.

Any excessive drain above these figures is usually due to shorting or wiring faults that keep circuits/devices energized when you turn them off.

These devices include computer modules, hidden lighting (glove compartment, trunk, or hood), headlights, and relay switches.

A vehicle’s electromagnetic relay switch

But the low power issue might not be due to the high amp draw. A faulty battery will not meet the power demands of a starter motor.

It can also be due to damaged alternator diodes. Alternators can have up to six diodes for AC to DC conversion to recharge the battery.

So if worn out, you won’t have a fully-charged battery.

Automotive Battery Failure/Battery Drain Signs

Batteries have a finite life. So if you have not replaced your car battery for about 4-5 years, it is most likely the culprit.

Slow battery drain will wear out healthy batteries faster, shortening their lifespan. So check for these signs to solve the issue quickly before the repair becomes more expensive.

Clicking Instead of Cranking

One of the signs of a dead battery is a lengthy cranking period or clicking sounds from the starter motor (starter relay).

Dashboard Lights Turn On, But the Engine Doesn’t Start

If too weak, the battery will not even crank the starter. So the dashboard lights and head unit will turn on, but the battery won’t have enough power to energize the starter motor.

Dim Headlights

A drained or faulty battery only holds a little charge, meaning it will provide low electrical current levels to power your headlights.

Backfiring

Gasoline engines use spark plugs to ignite the air-fuel mix. A low or failing battery might supply irregular power to the ignition system, causing intermittent sparks.

So the fuel might not burn in the combustion chamber.

Vehicle Needs Jump Starting

Jump starting is typical when the battery is on its last legs or drained low.

Wrap Up

Parasitic battery drain issues have similar symptoms as dead or failing batteries. So you need to diagnose this problem from three angles.

Check the battery status, alternator charging system, and fuse box current drain.

Once you’ve narrowed down the problem, fix and re-test the system. Remember, the excessive drain can damage the battery.

So we recommend solving battery drain issues immediately after you notice the symptoms above.