Is your BMW E90 key fob acting up, especially when the temperature drops? You might be experiencing the common issue of a dying key fob battery. If you’ve noticed your key fob struggling to lock or unlock your car, or if your BMW is not saving your personalized settings when starting in cold weather, the battery is likely the culprit. Instead of rushing to a dealership and spending a hefty sum, you can easily replace the battery yourself. This guide will walk you through the process of replacing your E90 Key Fob Battery, saving you time and money.
What You’ll Need
Before we begin, gather these essential items:
- Replacement Battery: It’s crucial to get the correct battery. For the BMW E90 key fob, you’ll need a VL2020 lithium-ion rechargeable battery with tabs at a 90-degree offset. You can find these online – a good source is this eBay link. Make sure to verify the terminal placement before purchase!
- Sharp X-Acto Knife or Precision Knife: For carefully opening the glued key fob casing.
- Non-Metallic Pry Tool: A credit card or plastic pry tool will work to gently lift the battery without short-circuiting anything.
- Soldering Iron and Solder: For desoldering the old battery and soldering in the new one.
- Optional: New Key Fob Housing: If your current housing is damaged or you want a fresh look.
- Optional: Cyanoacrylate Glue (Gel type): If you’re reusing the original housing to re-seal it.
Step-by-Step Battery Replacement Guide
Let’s get started with the battery replacement process. Work in a well-lit area and take your time to avoid damaging the key fob’s internal components.
Step 1: Carefully Open the Key Fob Casing
The BMW E90 key fob is sealed with strong glue. Using your sharp X-Acto knife, carefully score along the seam line of the fob. Apply gentle pressure and make multiple passes rather than trying to force it open in one go. Important: Do not cut too deep! The circuit board (PCB) is directly underneath the plastic, and you risk damaging it if you apply too much pressure or cut too deeply. Patience is key here. Work your way around the entire seam until you can gently pry the two halves apart.
Step 2: Desoldering the Old Battery
Once the fob is open, you’ll see the PCB with the battery soldered in place. To remove the old e90 key fob battery, you’ll need to desolder it. Take your non-metallic pry tool (like a credit card) and gently apply a small amount of upward pressure to the corner of the battery.
Now, apply heat to the corner terminal of the battery with your soldering iron. Once the solder melts, the corner terminal should lift slightly due to the pressure from your pry tool. Repeat this for the other terminal. It’s generally easier to start with the corner terminal because the middle terminal has a longer lead, making it harder to get under for leverage initially. Be careful not to apply excessive heat to the PCB, as this could damage the delicate components.
Step 3: Soldering in the New Battery
With the old battery removed, it’s time to install the new e90 key fob battery. Place the new VL2020 battery into the battery holes on the PCB. Hold the PCB by its edges and gently press down on the battery to ensure the terminals are properly seated.
Apply heat to the middle terminal of the new battery with your soldering iron, allowing the solder to flow and secure the connection. Then, repeat this process for the corner terminal. Ensure you get a good solder joint on both terminals for a reliable connection. Avoid using excessive solder, as this can create bridges or cold solder joints.
Step 4: Test and Reassemble
Before permanently sealing the key fob, it’s crucial to test if the new battery is working correctly. Dry fit the PCB back into the key fob housing and test all the key functions: locking, unlocking, and remote start (if applicable). If everything works as expected – congratulations! You’ve successfully replaced your e90 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 key fob housing for a pristine finish and easy snap-together reassembly. Alternatively, if you’re happy with your current housing, you can glue it back together. If using glue, apply a small amount of gel-type cyanoacrylate glue sparingly along the seam. Gel glue is recommended as it’s less likely to run and seep into unwanted areas. Press the two halves of the housing firmly together and allow the glue to dry completely. Avoid getting glue on the PCB or buttons.
Conclusion
Replacing your e90 key fob battery is a straightforward DIY task that can resolve common key fob issues and save you money. By following these steps and taking your time, you can restore your key fob to full functionality and avoid costly dealership service. Remember to always use the correct VL2020 battery and handle the internal components with care. Enjoy the peace of mind knowing you’ve tackled this common BMW maintenance item yourself!
