The Ultimate Guide on How to Test Battery Draws

Is your car battery drained overnight? If so, then one thing for sure is are some accessories or electrical equipment that draw electricity from your car battery even when your engine is not running. If the electrical draws are big, it's enough to cause your battery to drain overnight while your car is parked. To identify which circuit is causing draws. here's a short video.

To test for car battery draws, also known as parasitic battery drains, you can follow these steps:

1. Preparation:

• Ensure that all electrical devices in the car are turned off, including headlights, interior lights, and accessories.
• Make sure the car's engine is turned off and the key is removed from the ignition.

2. Disconnect the negative battery cable:

• Locate the car's battery under the hood.
• Identify the negative terminal, usually marked with a "-" sign.
• Using a wrench or socket, loosen the nut on the negative terminal.
• Carefully remove the negative battery cable from the terminal and set it aside. Be cautious not to let it come into contact with any metal surfaces.

3. Connect an ammeter:

• Obtain a multimeter or digital ammeter capable of measuring DC current.
• Set the ammeter to measure DC current in the milliamp (mA) range.
• Connect the positive (red) lead of the ammeter to the negative battery terminal.
• Connect the negative (black) lead of the ammeter to the negative battery cable that you previously disconnected.

4. Observe the current reading:

• With the ammeter connected, you're now measuring the current draw from the battery.
• Wait for a few minutes to allow the car's systems to enter sleep mode.
• Take note of the current reading displayed on the ammeter. Ideally, the reading should be very low, typically in the range of a few milliamps (e.g., 20-50mA).

5. Identify abnormal current draw:

• If the current draw is excessively high (e.g., several hundred milliamps or more), there may be a parasitic drain in the car's electrical system.
• To identify the source of the drain, you can start removing and reinserting fuses one by one while monitoring the ammeter reading.
• When you remove a fuse and notice a significant drop in the current reading, you have likely found the circuit causing the drain.

6. Troubleshoot the cause:

• Once you've identified the circuit, consult the car's owner manual or a wiring diagram to determine which devices or components are connected to that circuit.
• Inspect the identified components for any signs of malfunction or wiring issues.
• If necessary, consult a professional mechanic or an automotive electrician to help diagnose and repair the problem.

Remember to exercise caution throughout the process and avoid short-circuiting the battery or causing any electrical damage. If you're unsure or uncomfortable performing the test yourself, it's always recommended to seek assistance from a qualified automotive professional.