2004 BMW 325i Key Fob Battery Replacement Guide

Are you experiencing issues with your 2004 BMW 325i key fob? Does it take multiple presses to lock or unlock your doors, or does the range seem significantly reduced? You might be dealing with a dying key fob battery. Many BMW owners encounter this problem, and thankfully, replacing the battery in your 2004 BMW 325i key fob is a straightforward DIY task that can save you a trip to the dealership and unnecessary expenses.

This guide will walk you through the process of replacing your 2004 Bmw 325i Key Fob Battery. We’ll cover everything from opening the notoriously glued-shut fob to re-soldering a new battery and re-syncing your key to your vehicle. No more struggling to get into your car – let’s get your key fob working like new again!

Symptoms of a Dying 2004 BMW 325i Key Fob Battery

Before diving into the replacement process, it’s helpful to confirm that a low battery is indeed the culprit. Here are common symptoms indicating your 2004 BMW 325i key fob battery is nearing the end of its life:

Reduced Range: You need to be much closer to your BMW for the key fob to function.
Intermittent Operation: Buttons become less responsive, requiring multiple presses to lock, unlock, or activate the trunk release.
Inconsistent Performance: The key fob works sometimes, but fails at other times, especially in colder weather.
Complete Failure: The key fob stops working altogether, even when standing right next to the car.

If you are experiencing these issues, replacing your 2004 BMW 325i key fob battery is likely the solution.

Tools Needed for 2004 BMW 325i Key Fob Battery Replacement

To successfully replace the battery in your 2004 BMW 325i key fob, gather the following tools:

Vice-Grip: To securely hold the key.
Paint Scraper: For initial prying and separating the fob halves.
Sharp Knife or Precision Blade: To carefully cut along the glued seam of the fob.
Small Flathead Screwdriver or Chisel: To help pry off the old battery leads.
Soldering Iron (Small Tip Recommended): For soldering the new battery leads.
Silver Solder: For creating a secure electrical connection.
Wide Jaw Pliers (Channel-Locks or Similar): To hold the PCB steady during soldering.
Rubber Band: To gently apply pressure to the pliers and secure the PCB.
New Panasonic VL2020 Battery with Leads (or Plain VL2020 Battery): The correct replacement battery for your 2004 BMW 325i key fob.
Plastic Glue: To re-seal the key fob case.
Clamps or Rubber Bands: To hold the fob halves together while the glue dries.

Step-by-Step 2004 BMW 325i Key Fob Battery Replacement Guide

Now, let’s get into the detailed steps for replacing your 2004 BMW 325i key fob battery:

1. Opening the Key Fob

The 2004 BMW 325i key fob is notoriously glued shut, requiring some careful effort to open.

Secure the Key: Use the vice-grip to firmly hold the metal key portion of the fob. This provides a stable base for working on the plastic casing.
Start Prying: Begin at the keyring end of the fob. Insert the paint scraper into the seam where the two halves of the plastic casing meet.
Slice and Pry: Use the sharp knife or precision blade to carefully slice along the seam of the fob while simultaneously prying with the scraper. Work your way around the perimeter of the fob, gently separating the glued halves. Take your time and avoid applying excessive force, which could damage the internal components.

Alt text: Opening a 2004 BMW 325i key fob. A paint scraper and knife are used to carefully separate the glued plastic casing to access the battery for replacement.

2. Battery Identification and Removal

Once the fob is open, you’ll see the internal circuit board (PCB) and the battery.

Identify the Battery: The original battery in a 2004 BMW 325i key fob is typically a Panasonic VL2020 with custom leads welded to it. Note its orientation and the position of the positive (+) and negative (-) terminals.
Prepare the PCB for Soldering: Grip the PCB with the wide jaw pliers, ensuring you don’t clamp down too tightly. Secure the pliers with a rubber band to maintain gentle pressure and keep your hands free for soldering.
Remove the Old Battery: Using the soldering iron, apply heat to the back of each battery lead where it is soldered to the PCB. Wait for the solder to melt, then gently pull the lead free from the board. Repeat this for both leads and carefully remove the old battery.
Detach Custom Leads (If Necessary): If you purchased a replacement Panasonic VL2020 battery without pre-attached leads, you’ll need to detach the custom leads from the old battery. Use a small chisel or knife to carefully pry them off. Be gentle to avoid damaging the leads, as you’ll reuse them. If your new battery comes with leads, you can skip this step.

Alt text: Internal view of a 2004 BMW 325i key fob after opening. The image highlights the PCB and the location of the VL2020 battery that needs replacement.

3. Soldering the New Battery

Now it’s time to install the new 2004 BMW 325i key fob battery.

Solder the Negative Lead: Solder the negative lead to the bottom (non-writing) side of the new VL2020 battery. Use a small amount of silver solder to create a good connection. Remember that the fit inside the fob is tight, so avoid using excessive solder.
Re-solder Negative Lead to PCB: Align the negative lead with its corresponding hole on the PCB (note that the negative lead’s through-pin is typically smaller). Re-solder the negative lead to the PCB, ensuring it sits correctly on the white insulating pad. Double-check the battery orientation before proceeding.
Solder the Positive Lead: Solder the positive lead to the remaining terminal of the battery and then to its designated point on the PCB. Ensure a solid solder connection for both positive and negative leads.

4. Reassembling the Key Fob

With the new battery soldered in place, it’s time to reassemble your 2004 BMW 325i key fob.

Clean Fob Edges: Inspect the edges of the fob casing and remove any frayed plastic or excess glue to ensure a clean and tight seal.
Test Fit (Without PCB): Before applying glue, try mating the two halves of the fob together without the PCB inside to ensure they fit properly.
Apply Glue: Apply a thin, even bead of plastic glue to the perimeter of one half of the fob casing.
Reassemble and Clamp: Carefully place the PCB back into the fob and align the two halves. Press them firmly together and use clamps or rubber bands to hold them securely while the glue dries completely, following the glue manufacturer’s recommended drying time.

Key Fob Re-Sequencing (Programming)

After replacing the 2004 BMW 325i key fob battery, you may need to re-sequence or re-program your key to ensure it communicates correctly with your vehicle. Follow these steps:

Prepare Keys: Gather all your BMW 325i key fobs. Designate one key as the “initial” key – this is simply for clarity during the process.
Enter Vehicle: Get inside your BMW 325i, close all doors, and ensure the doors are unlocked.
Ignition Position 2: Insert the initial key into the ignition and turn it to position 2 (all dashboard lights are on, but the engine is not started).
Remove Key and Button Press Sequence: Remove the key from the ignition. Immediately press and hold the unlock button on the key fob. While holding the unlock button, press the lock button three times in quick succession. Then, release all buttons.
Vehicle Response: The car’s Central Locking System (CLS) should respond by locking and then unlocking the driver’s door. This confirms the key has been re-sequenced.
Repeat for Additional Keys: For each additional key fob, repeat step 4 (button press sequence) within 30 seconds of the previous key.

Important Note: Any key fobs not re-sequenced during this process will not function correctly and will need to be included in a future re-sequencing procedure.

Conclusion

Replacing the battery in your 2004 BMW 325i key fob is a manageable DIY project. By following these steps and taking your time, you can restore your key fob’s functionality and avoid unnecessary dealership costs. With a fresh 2004 BMW 325i key fob battery, you can once again enjoy the convenience of remote locking, unlocking, and trunk access for your vehicle.