How to Replace the Battery in a BMW Diamond Key for the E46

Introduction

Replacing the battery in a BMW diamond key, especially for the E46 3-series models from 1998 to 2005, is a complex task. However, with some patience and the right tools, you can do it yourself. This guide will walk you through the process step-by-step.

Tools and Materials Needed

• Box cutter
• Soldering iron
• Soldering vacuum
• Small tweezers
• Superglue
• Replacement battery (VL 2020)

Step 1: Separate the Key Fob

The first step is to separate the key fob into two halves. Look for a line around the edge of the key fob that divides it into two pieces.

Scoring the Key Fob

Using a box cutter, score all the way around the line. This process may take some time, possibly five to ten minutes, especially if you want to keep the key fob as intact as possible. The best place to start is at the top, where you can get some leverage.

Breaking Through the Plastic

Continue to cut through the plastic until you can see the box cutter penetrating the key fob. Once you’ve scored all the way around, you should be able to separate the two halves of the key fob.

Step 2: Access the Circuit Board and Battery

Once the key fob is open, you’ll have access to the circuit board and the battery inside.

Removing the Circuit Board

Carefully remove the circuit board using small tweezers. There are two points where the circuit board connects to the key fob. Gently tap or pull it out.

Identifying the Battery

The battery you need to replace is the VL 2020, a rechargeable battery. It charges when the key is in the ignition, but if it dies, you’ll need to replace it.

Step 3: Desolder the Old Battery

To replace the battery, you’ll need to desolder it from the circuit board. The battery is attached at two points, known as the legs.

Using the Soldering Iron

Heat up the soldering iron and use it to melt the solder at the two points where the battery legs are attached. Use the soldering vacuum to suck up the melted solder.

Removing the Battery

Once the solder is removed, you should be able to pull the battery off the circuit board. If there’s still some solder left, you can melt it and let it drop through.

Step 4: Install the New Battery

Now it’s time to install the new VL 2020 battery.

Positioning the New Battery

Make sure the new battery has legs that are offset 90 degrees, not 180 degrees, to match the circuit board. Insert the legs into the two points where the old battery was attached.

Resoldering the Battery

Use the soldering iron to solder the new battery’s legs to the circuit board. Ensure the solder is secure and the battery is firmly attached.

Step 5: Reassemble the Key Fob

Once the new battery is installed, it’s time to reassemble the key fob.

Reinserting the Circuit Board

Place the circuit board back into its correct position. Ensure the buttons align properly with the button side of the key fob.

Sealing the Key Fob

Apply superglue around the edges of the key fob and press the two halves together. Hold them in place until the glue sets.

Conclusion

By following these steps, you can replace the battery in your BMW diamond key for the E46 3-series models. This process may seem daunting, but with patience and the right tools, you can do it yourself and save money on a replacement key fob.

FAQ

What tools do I need?

You will need a box cutter, soldering iron, soldering vacuum, small tweezers, superglue, and a replacement battery (VL 2020).

How long does this process take?

Scoring the key fob can take five to ten minutes. The entire process may take around 30 minutes to an hour, depending on your experience.

Can I use any battery?

No, you need to use a VL 2020 rechargeable battery. Ensure it has legs offset at 90 degrees.

Is it safe to do this myself?

Yes, but be careful when using the box cutter and soldering iron. Follow the steps carefully to avoid damaging the key fob.

What if I don’t have a soldering iron?

You can purchase one online for around $19. It’s a useful tool for various DIY projects.

Can I use regular glue instead of superglue?

Superglue is recommended for a secure seal, but strong adhesive glue may also work.

What if the new battery doesn’t fit?

Ensure the new battery has legs offset at 90 degrees. If it still doesn’t fit, double-check the battery model and alignment.

Do I need to program the key fob after replacing the battery?

No, the key fob should work as usual once the new battery is installed and the fob is reassembled.