2005 BMW Key Fob Battery Replacement: A Step-by-Step Guide

Is your 2005 BMW key fob starting to act up? Experiencing issues like needing to press buttons multiple times or having to be right next to your car for it to respond? You might be dealing with a dying key fob battery. Forget the urban legend that your BMW key fob battery recharges itself while driving – that’s simply not true. The reality is, like any battery, the one in your BMW key fob will eventually need replacing.

This guide will walk you through the process of replacing the battery in your 2005 BMW key fob. It’s a DIY task that can save you a trip to the dealership and some money. Let’s get started!

Symptoms of a Low Key Fob Battery

Before diving into the replacement, let’s confirm if a weak battery is indeed the culprit. Common signs of a low 2005 BMW key fob battery include:

• Reduced Range: You need to be closer to your BMW than usual for the key fob to lock or unlock the doors.
• Intermittent Operation: Buttons become less responsive, requiring multiple presses to activate functions.
• No Response: In the worst case, the key fob might stop working altogether, even when you’re inside the car.

If you’re experiencing these issues, replacing the battery is likely the solution.

Tools You’ll Need for the Replacement

Replacing your BMW key fob battery requires a few basic tools. Gather these items before you begin:

• Vice-Grip: To securely hold the key.
• Paint Scraper: For initial prying to start opening the glued fob.
• Sharp Knife: A utility knife or similar for carefully slicing along the fob seam.
• Small Flathead Screwdriver or Chisel: To further pry open the fob and separate the halves.
• Soldering Iron (Small Tip): For desoldering and soldering the battery leads.
• Silver Solder: For making secure electrical connections.
• Wide Jaw Pliers (Channel-Locks): To hold the circuit board steady.
• Rubber Band: To apply gentle pressure to the pliers.
• New Panasonic VL2020 Battery with Leads (or similar): While pre-leaded batteries are convenient, a plain VL2020 battery and soldering skills will also work.
• Plastic Glue: To re-seal the key fob case.
• Clamps or Rubber Bands: To hold the fob together while the glue dries.

Step-by-Step 2005 BMW Key Fob Battery Replacement Guide

Now, let’s proceed with the battery replacement. Follow these steps carefully:

Step 1: Opening the Key Fob

The 2005 BMW key fob is notoriously glued shut, so opening it requires patience and care.

1. Secure the Key: Use the vice-grip to firmly hold the metal key part of the fob. This provides leverage and stability.
2. Start Prying: Begin at the ring end of the fob. Insert the paint scraper into the seam where the two halves of the plastic case meet.
3. Slice and Pry: Carefully use the sharp knife to slice along the seam of the fob case. Simultaneously, gently pry with the knife or scraper to start cracking the case open. Work your way around the perimeter of the fob, being patient and applying steady pressure. Avoid excessive force to prevent damage to the plastic.

Alt text: Close-up showing a paint scraper and knife being used to carefully open a 2005 BMW key fob along its glued seam.

4. Separate the Halves: Once you’ve worked around the entire seam, you should be able to carefully pry the two halves of the key fob case apart. Use the small flathead screwdriver or chisel if needed to gently assist in separating the halves.

Step 2: Identifying the Battery

With the fob open, you’ll see the internal components.

1. Locate the Battery: The battery is a Panasonic VL 2020 (or equivalent) and is situated on one side of the printed circuit board (PCB). It’s typically held in place by soldered leads.
2. Observe the Battery Orientation: Note the orientation of the battery and the positive (+) and negative (-) terminals before removal. This is crucial for installing the new battery correctly. The negative lead is usually on the upper left, and the positive lead is on the upper right, as seen from the battery well side.

Alt text: Internal components of a 2005 BMW key fob after opening, highlighting the Panasonic VL2020 battery and the printed circuit board (PCB).

Step 3: Desoldering the Old Battery

Now, you’ll need to remove the old battery.

1. Secure the PCB: Grip the PCB with the wide jaw pliers to hold it steady. Use a rubber band around the handles of the pliers to maintain gentle pressure without overtightening, which could damage the board.
2. Desolder the Leads: Apply the hot soldering iron to the back of each battery lead where it’s soldered to the PCB. Wait for the solder to melt, then gently pull the lead free from the board. Repeat for both positive and negative leads.
3. Remove Old Battery: Once both leads are desoldered, carefully remove the old battery from the fob.
4. Remove Leads from Old Battery (If Necessary): If you purchased a plain VL2020 battery without pre-attached leads, you’ll need to carefully remove the custom leads from the old battery using a chisel or knife. Be gentle to avoid damaging the leads if you plan to reuse them. However, it is generally easier to purchase a new battery with leads already attached.

Step 4: Soldering the New Battery

Install the new battery in place of the old one.

1. Solder Negative Lead First: Solder the negative lead of the new battery to the correct pad on the PCB. The negative lead typically has a smaller through-pin. Ensure correct orientation by referring to your notes from Step 2 and the markings on the PCB.
2. Position the Battery: After soldering the negative lead, the battery should sit securely in the middle of the white insulating pad on the PCB.
3. Solder Positive Lead: Solder the positive lead to its corresponding pad on the PCB. It doesn’t matter if you solder the battery end or the board end first, as long as both connections are solid.
4. Check Solder Joints: Ensure both solder joints are clean and secure. Avoid using excessive solder, as space inside the fob is limited.

Step 5: Reassembling the Key Fob

With the new battery soldered in, it’s time to reassemble the key fob.

1. Clean Fob Edges: Clean any frayed edges or old glue from the inside of the fob case halves to ensure a clean and tight seal.
2. Test Fit: Before applying glue, do a test fit of the fob halves with the PCB inside to make sure they mate correctly and close properly.
3. Apply Glue: Apply a thin, even bead of plastic glue to the perimeter of one half of the fob case.
4. Clamp the Fob: Carefully align and press the two halves of the fob together. Use clamps or rubber bands to firmly hold the fob closed while the glue dries, following the glue manufacturer’s recommended drying time.

Re-sequencing Your BMW Key Fob

After replacing the battery, you may need to re-sequence your key fob to your BMW. Here’s how:

1. Prepare Keys: Gather all BMW key fobs you have for your car.
2. Enter Vehicle: Get into your BMW, close all doors, and ensure the doors are unlocked.
3. Initial Key Insertion: Insert the first key you want to re-sequence into the ignition.
4. Turn to Position 2: Turn the key to position 2 (ignition on, all dash lights illuminated, but engine not started).
5. Remove Key and Button Press: 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. Release all buttons.
6. Check for Response: The car’s central locking system should respond by locking the doors and then unlocking the driver’s door to confirm successful sequencing.
7. Repeat for Other Keys: For each additional key fob, repeat step 5.

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

Conclusion

Congratulations! You’ve successfully replaced the battery in your 2005 BMW key fob. By following these steps, you’ve not only saved money but also gained a valuable DIY skill. Enjoy the renewed responsiveness of your key fob and the peace of mind knowing you tackled this car maintenance task yourself.