Umair Gaines
A parasitic battery drain, or draw, occurs when there is an excessive electrical current draining from a vehicle's battery when the engine is off. This can be caused by anything from a dimming dome light left on or a faulty aftermarket radio, to alarm wiring or GPS systems. To test for a parasitic draw, a digital multimeter is connected to the negative battery terminal of the vehicle, and fuses are removed one at a time while observing the multimeter's reading. This process can help identify the electrical circuit causing the parasitic draw. Additionally, it is important to ensure regular vehicle use, maintain clean and secure battery connections, and periodically check the electrical system to prevent parasitic drain.
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What You'll Learn
Parasitic battery drain
Most vehicles experience a "normal" amount of parasitic battery drain, typically between 50 and 85 milliamps in newer cars and less than 50 milliamps for older cars. However, excessive parasitic battery drain can be caused by a variety of factors, including short circuits, electrical devices that remain energised, and faulty batteries or alternator diodes.
To check for parasitic battery drain, follow these steps:
- Park the vehicle in a safe and well-ventilated area, ensuring all lights, accessories, and electrical systems are turned off.
- Use a vehicle battery charger to charge the battery to 100%.
- Disconnect the negative cable from the battery terminal using a wrench or socket.
- Connect a digital multimeter to the negative battery cable and terminal.
- Locate the fuse box and remove the fuses one at a time, checking the multimeter for any changes in the reading.
- When pulling a fuse causes the multimeter reading to drop significantly, you've found the electrical circuit causing the parasitic draw.
- Consult the chart on the fuse box, owner's manual, or wiring diagram to identify the specific component or system responsible for the parasitic drain.
It's important to regularly inspect your vehicle's electrical systems and components for any signs of malfunction or damage, ensuring all connections are secure and no loose wires could trigger short circuits. Additionally, consider investing in a battery disconnect switch or regularly charging your battery to prevent parasitic drain during extended periods of vehicle storage.
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Using a multimeter
To check for battery drain, you need to measure the parasitic draw by setting the multimeter to the correct amperage mode and connecting it in series with the battery. Here is a step-by-step guide:
Prepare the vehicle:
- Park the vehicle in a safe and well-ventilated area.
- Ensure all lights, accessories, and electrical systems are turned off.
- Wait for at least 20 minutes to allow the vehicle's modules to enter sleep mode.
- Fully charge the battery before starting. Voltage would be around 12.6V for a good battery.
Set up the multimeter:
- Switch the multimeter to DC Ampere (A) mode.
- Set the range to a suitable value higher than the expected current draw (usually in milliamperes or mA). Start with a range of 10A if available.
- Plug the black lead into the COM (common) port.
- Plug the red lead into the 10A or the highest amperage port (not the voltage port).
Connect the multimeter:
- Open the vehicle's hood and locate the battery.
- Disconnect the negative battery cable. Using a wrench or socket, loosen and remove the negative (-) battery cable from the battery terminal.
- Connect the multimeter leads in series between the negative battery terminal and the negative battery cable. Connect the red lead to the battery terminal and the black lead to the battery cable.
Conduct the test:
- Once the multimeter is connected, determine which electrical component is responsible for the drain.
- Refer to the owner's manual to find the fuse box location. Common locations include under the dashboard, engine bay, or near the glove compartment.
- While monitoring the multimeter's current reading, remove one fuse at a time using fuse pullers or needle-nose pliers. Watch for a drop in the reading.
- Once you find the fuse causing the drain, check what electrical system it corresponds to (e.g. interior lights, radio, security system).
Reassemble and retest:
- After resolving the issue, reinsert any removed fuses and reconnect the negative battery cable.
- Double-check that all connections are secure.
- Perform the same current draw test again to ensure that the parasitic draw has been eliminated or reduced to an acceptable level.
If you are unsure or uncomfortable with performing these steps, it is recommended to seek assistance from a qualified automotive technician or a professional mechanic.
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Test light
A test light can be used to check for electrical draining of a battery. This is a simple process of elimination that can help identify the circuit causing the battery drain.
Firstly, ensure that the battery is fully charged. Then, disconnect the negative battery cable and connect the test light between the negative cable and the negative battery post. Make sure that the test light has a real bulb inside and is not an LED test light. With the doors shut and all accessories turned off, if the test light is lit, there is a drain on the battery.
The next step is to remove one fuse at a time from the fuse block, checking each time to see if the test light has gone out. When you remove the fuse that makes the test light go out, you have found the circuit causing the battery drain. If the light does not go out after removing all the fuses, the alternator may be the problem or it may be wired incorrectly. To check this, conduct the same test after completely disconnecting the alternator wiring.
After identifying and resolving the issue, reinsert any removed fuses and reconnect the negative battery cable. Double-check that all connections are secure and perform the same current draw test again to ensure that the battery drain has been eliminated.
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Battery maintenance
Regularly Inspect and Clean the Battery:
- Check the battery terminals for any signs of corrosion or dirt buildup.
- Clean the terminals using a mixture of baking soda and water if necessary.
- Ensure that the battery case is dry and clean, as moisture and dirt can lead to battery drain issues.
Check for Loose Connections:
- Verify that the positive and negative terminals connected to your battery are secure and have not come loose over time.
- Loose connections can hinder the battery's ability to transmit power effectively.
Prevent Parasitic Battery Drain:
- Parasitic battery drain occurs when electrical components or accessories continue to draw power from the battery even when the vehicle is turned off.
- To prevent this, make sure all lights, electronic devices, and accessories are turned off or unplugged when not in use.
- Ensure that your vehicle's doors, trunk, and glove box are fully closed and latched.
- If you plan to park your vehicle for an extended period, consider unplugging unnecessary accessories and taking your car for a drive once a week to keep the battery charged.
Monitor Battery Age and Performance:
- Batteries typically last up to five years, but this can vary depending on usage conditions and environmental factors.
- Keep track of how long you've had your battery and consider replacing it if it's more than five years old or if it struggles to hold a charge.
Diagnose and Resolve Electrical Drains:
- If you suspect an electrical drain, you can use a digital multimeter to identify the source.
- Connect the multimeter to the negative battery terminal and remove fuses one at a time, watching for changes in the multimeter reading.
- If you identify a specific circuit or component causing the drain, repair or replace it as needed, and ensure the multimeter reading returns to acceptable levels.
Remember, if you're uncomfortable performing any of these maintenance tasks, you can always seek assistance from a qualified automotive technician or electrician.
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Battery disconnect switch
If you're experiencing battery drain, there are a number of ways to check what's causing it. Firstly, you can test for a parasitic draw, which is when an excessive electrical current drains from a vehicle's battery when the engine is off. To do this, you can use a digital multimeter, which is better than an analogue one for accuracy. You can also use a test switch, which enables you to restart the engine.
Now, if you're looking to prevent battery drain, a battery disconnect switch may be useful. This is a device that can be used to disconnect the battery from a circuit, effectively cutting off the power supply. This can be useful if you're working on a vehicle or if you want to prevent battery drain when the vehicle is not in use.
There are a variety of battery disconnect switches available on the market, with different features and specifications. Some switches have a higher amperage rating than others, which is important to consider depending on the current draw of your vehicle. You can also find switches with different voltage ratings, ranging from 6 to 36 volts. Some switches have a lever actuation type, while others have a knob. It's important to choose a switch that is compatible with your vehicle's electrical system.
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Frequently asked questions
You can use a multimeter to test for a parasitic draw, which refers to an excessive electrical current draining from a vehicle's battery when the engine is off. First, ensure your battery is fully charged. Then, disconnect the negative battery cable and connect the multimeter in series with the negative terminal and the disconnected cable. Finally, turn off all electrical components and check for any components still drawing power.
A parasitic draw, also known as a parasitic drain, occurs when there is a continuous small drain on the battery due to electrical components being left on or faulty wiring. This can cause the battery to drain in a matter of days.
To locate the source of a parasitic draw, you can use a process of elimination by removing fuses one at a time while monitoring the multimeter's reading. When the reading drops significantly, you've found the electrical circuit causing the parasitic draw. You can then consult the fuse box chart and/or the owner's manual to identify the specific component causing the issue.
