Modern vehicles like the 2009 Audi A4 rely heavily on their electrical systems, making a healthy battery crucial for optimal performance. If you’re experiencing electrical issues such as dimming headlights or key fob malfunctions with your 09 Audi A4, a failing battery could very well be the culprit. While battery replacement might seem straightforward in many cars, the Audi A4 presents a slightly unique process. One of the first challenges is understanding the 09 Audi A4 Battery Location. Unlike many vehicles where the battery is under the hood, in the Audi A4 B8 model, it’s tucked away in a less conventional spot. This guide will walk you through the process of locating and replacing the battery in your 2009 Audi A4.
Before you begin, ensure you have the necessary tools and a replacement battery that is compatible with your Audi A4. It’s important to note that Audi A4s often require OEM (Original Equipment Manufacturer) batteries and may need computer reprogramming after installation for the vehicle to properly recognize the new battery. While you can perform the physical replacement yourself, you might need to visit a dealership or use diagnostic software like VCDS for the reprogramming aspect.
Materials Needed
- Replacement genuine Audi battery (check for compatibility with your 2009 A4 model)
- Ratchet
- 10mm socket
- 13mm socket
Step-by-Step Guide to Accessing and Replacing Your 09 Audi A4 Battery
The battery in your 09 Audi A4 is located in the trunk, beneath the spare tire. Follow these steps to access and replace it:
Step 1 – Accessing the Battery
Open the trunk of your Audi A4 and lift the trunk floor panel to reveal the spare tire compartment. You’ll first need to remove the spare tire and tool tray to get to the battery location.
- Locate the large wingnut in the center of the spare tire. Twist this wingnut counterclockwise to loosen and remove it.
- Once the wingnut is removed, you can lift and remove the spare tire from the trunk. Set the spare tire aside in a safe place.
- After removing the spare tire, you’ll see a spare tire tray. Lift this tray out and set it aside as well.
- Underneath the spare tire tray, you will find a tool tray. Lift out the tool tray and set it aside. Now you should have a clear view and access to the battery of your 09 Audi A4.
Figure 1. Removing the spare tire to access the Audi A4 battery location.
Figure 2. Removing the tool tray to fully expose the battery compartment in the Audi A4.
Step 2 – Removing the Battery Brackets
With the battery now accessible, the next step is to remove the brackets that secure it in place.
- Use your 13mm socket and ratchet to locate and remove the bolts securing the main battery bracket. There are typically four bolts for this bracket. Remove all four bolts completely.
- Once the bolts are removed, take off the main battery bracket.
- You will find another, smaller bracket at the base of the battery. This bracket is usually held in place by a single 13mm bolt. Use your 13mm socket to remove this bolt and then remove the smaller bracket.
Figure 3. Removing the battery bracket to free the battery for removal in the Audi A4.
Step 3 – Disconnecting the Old Battery
Now that the battery is free from its brackets, you can disconnect the old battery.
- Locate and disconnect the vacuum hose connected to the side of the battery. Gently pull it off to disconnect.
- Using your 10mm socket, loosen the clamp on the negative (black) battery cable. Once loose, carefully pull the clamp off the negative terminal. Move the cable aside, ensuring it cannot accidentally touch the battery terminal to prevent short circuits.
- Repeat the previous step for the positive (red) battery cable. Loosen the clamp with the 10mm socket, remove it from the positive terminal, and safely move the cable aside.
- With both battery cables and the vacuum hose disconnected, carefully lift the old battery out of its location in the trunk. Batteries can be heavy, so lift with caution and move it to a safe, dry location for disposal.
Figure 4. Disconnecting the vacuum hose from the Audi A4 battery.
Figure 5. Disconnecting the positive and negative battery cables on the Audi A4.
Pro Tip: Remember to responsibly dispose of your old car battery. Most auto parts stores, dealerships, and battery retailers offer battery recycling programs.
Step 4 – Installing the New Battery
With the old battery removed, you are ready to install the new one.
- Carefully place the new battery into the battery compartment in the trunk, ensuring that the terminal posts are oriented correctly to align with the positive and negative battery cables.
- Reconnect the vacuum hose to the new battery.
- Reattach the positive (red) battery cable first, ensuring the clamp is securely tightened with your 10mm socket.
- Next, reconnect the negative (black) battery cable and tighten its clamp securely as well.
- Important: Before reassembling everything, locate and write down the BEM (Battery Energy Management) code on your new battery. This code is crucial for the car’s computer to recognize the new battery and is usually composed of two serial numbers and a vendor identifier.
Figure 6. Locating and recording the BEM code from the new Audi A4 battery. Note the two serial numbers and vendor identifier.
- Reinstall the smaller battery bracket and tighten its 13mm bolt.
- Replace the main battery bracket and tighten all four 13mm bolts to secure it.
- Put back the tool tray, spare tire tray, and finally, the spare tire into the trunk. Secure the spare tire with the wingnut, tightening it clockwise. Replace the trunk floor panel.
Your 09 Audi A4 should now start and run with the new battery. However, it may operate in a low power mode until the car’s computer is properly coded to recognize the new battery.
Pro Tip: If you have access to VCDS software or a similar diagnostic tool, you can code the new battery yourself. Navigate to control module 61 (Battery Regulation), then to “Coding,” and select “Battery coding.” Input the BEM code you recorded earlier to properly register the new battery with your Audi A4’s system. This ensures optimal battery management and charging.
