Are you experiencing issues with your 2008 BMW 335i key fob, especially in cold weather? Many BMW owners find that their key fob becomes unreliable when temperatures drop, leading to problems with locking, unlocking, and even remembering personalized car settings. If your key fob is acting up, particularly with symptoms like reduced range or settings resetting, a battery replacement might be the solution. This guide will walk you through replacing the battery in your 2008 BMW 335i key fob yourself, saving you time and money compared to dealership service.
Before you begin, gather the necessary tools and the correct replacement battery. You’ll need a sharp X-acto knife, a non-metallic pry tool (like a credit card), a soldering iron, and the appropriate VL2020 battery. It’s crucial to purchase the correct battery type to ensure proper function and longevity of your key fob.
Step-by-Step 2008 BMW 335i Key Fob Battery Replacement
Step 1: Purchase the Correct Battery
The 2008 BMW 335i key fob requires a specific type of battery: the VL2020. This is a lithium-ion rechargeable battery with a 90-degree terminal offset. You can find these batteries online from various retailers. Ensure you are purchasing a genuine VL2020 battery for optimal performance. A reliable source for purchasing the correct battery is this eBay link.
Step 2: Carefully Open the Key Fob
The BMW key fob is sealed shut and requires careful opening. Using a sharp X-acto knife, gently score along the seam of the key fob casing. Work slowly and patiently, avoiding excessive pressure to prevent damage to the internal circuit board (PCB). Multiple light passes are better than trying to force it open in one go. Take your time to carefully separate the top and bottom halves of the fob.
Step 3: Desolder the Old Battery
Once the key fob is open, you’ll see the PCB with the battery soldered in place. To remove the old battery, you’ll need to desolder it. Using a non-metallic pry tool, such as a credit card, gently apply a small amount of upward tension to the battery. Then, apply heat to the corner terminal of the battery with your soldering iron. Once the solder melts, the corner terminal should release. Repeat this process for the other terminal to fully remove the old VL2020 battery. Starting with the corner terminal is recommended as it provides space to maneuver the pry tool for the other terminal.
Step 4: Solder in the New Battery
With the old battery removed, it’s time to install the new VL2020 battery. Place the new battery into the battery holes on the PCB, ensuring correct polarity and terminal alignment. Hold the PCB by its edges and gently press down on the new battery to ensure the terminals make good contact with the solder pads. Apply heat to the middle terminal first, then the corner terminal, allowing the battery terminals to push through the existing solder and securely seat into place. Ensure a good solder joint for reliable power.
Step 5: Test and Reassemble
Before fully reassembling the key fob, perform a test. Dry fit the PCB back into the key fob housing and test the key’s functions – locking, unlocking, and starting the car. Also, check if your personalized settings are now being saved. If everything is working correctly, you’ve successfully replaced the battery! Now, you can either purchase a new key fob housing for a fresh look or simply glue the original housing back together. If you choose to glue it, use a gel-type cyanoacrylate glue sparingly to avoid it running and potentially damaging the PCB or gluing the PCB to the housing itself.
Replacing your 2008 BMW 335i key fob battery is a straightforward DIY task that can resolve common key fob issues, especially those exacerbated by cold weather. By following these steps, you can restore your key fob’s functionality and avoid unnecessary dealership costs.
