Experiencing issues with your 2008 BMW 5 Series key fob, especially in cold weather? You’re not alone. Many BMW owners find that their key fobs become less responsive when temperatures drop, often struggling to lock or unlock doors remotely. Furthermore, you might notice your car failing to recall personalized settings like radio presets when starting after a cold spell. The likely culprit? A dying key fob battery. Fortunately, replacing the battery in your BMW 5 Series key fob is a straightforward DIY task that can save you a trip to the dealership and keep your key working perfectly. This guide will walk you through each step to successfully replace your 2008 BMW 5 Series key fob battery.
Before you begin, you’ll need to gather a few items and the correct replacement battery. The battery you’ll need is a VL2020 lithium-ion rechargeable battery, specifically designed for BMW key fobs. It’s crucial to purchase the correct battery type to ensure proper function and longevity. You can find these online from reputable retailers. Alongside the battery, you’ll need a sharp X-acto knife or similar precision cutting tool to open the key fob casing, and a desoldering tool and soldering iron for the battery replacement itself. A non-metallic prying tool, like an old credit card or plastic spudger, will also be helpful to gently lift the battery without damaging the internal components.
Once you have your tools and replacement VL2020 battery ready, you can proceed with the battery replacement. The first and most delicate step is opening the key fob casing. BMW key fobs are typically glued shut, requiring careful and patient work to open them without causing damage.
Step 1: Carefully Open the Key Fob Casing
Using your sharp X-acto knife, gently start to cut along the seam where the two halves of the key fob casing meet. It’s essential to apply light pressure and make multiple passes rather than trying to force it open in one go. Work your way around the entire perimeter of the key fob. Be extremely cautious not to cut too deep, as the internal circuit board (PCB) sits directly beneath the casing and can be easily damaged if you apply too much pressure. Patience is key here. Take your time to separate the glued halves of the fob.
Step 2: Desolder the Old Battery
With the key fob casing open, you’ll see the circuit board and the old battery. Before attempting to remove the battery, it’s helpful to use a non-metallic pry tool, such as a credit card, to gently apply a small amount of upward tension to the battery. This will make it easier to desolder the terminals. Identify the battery terminals that are soldered to the PCB. It’s generally easier to start with the corner terminal. Apply heat from your soldering iron to the solder joint of the corner terminal while gently pulling upwards with your pry tool. Once the solder melts and the corner terminal is free, repeat this process for the remaining terminal. The middle terminal might have a longer lead, so removing the corner one first provides more space.
Step 3: Solder in the New VL2020 Battery
Now, take your new VL2020 battery and carefully align it with the battery holes on the PCB. Place the battery in position and hold the PCB from the edges. Gently apply a bit of downward force onto the battery to ensure good contact with the solder pads. Apply heat from your soldering iron to the middle terminal first, allowing the existing solder to melt and secure the battery terminal in place. Repeat this process for the corner terminal. Ensure that the battery is securely soldered to the PCB.
Step 4: Test and Reassemble Your Key Fob
Before permanently sealing the key fob, it’s crucial to test if the new battery is working. Dry fit the PCB back into the key fob housing and test the key fob’s functions – lock, unlock, and comfort access if applicable. If everything works as expected, congratulations! You have successfully replaced your 2008 BMW 5 Series key fob battery. If it doesn’t work, double-check your soldering connections and battery orientation.
For reassembly, you have a couple of options. You can purchase a new replacement key fob housing for a fresh look. Alternatively, if you prefer, you can simply glue the original housing back together. If choosing to re-glue, use a gel-type cyanoacrylate glue sparingly. Gel glue is less likely to run and minimizes the risk of accidentally gluing the PCB to the housing. Apply a small amount of glue to the edges of the casing and carefully press the two halves back together, holding them firmly until the glue sets.
Replacing your 2008 BMW 5 Series key fob battery is a cost-effective and satisfying DIY project. By following these steps, you can restore your key fob’s functionality and avoid unnecessary dealership expenses. Enjoy the reliable operation of your key fob, even in cold weather!
