Is your 2003 BMW 325i key fob acting up? Are you finding yourself pressing the buttons multiple times, or needing to be right next to your car for it to respond? You’re likely experiencing a dead or dying key fob battery. Many BMW owners encounter this issue, and while some might rush to a dealership, replacing the battery yourself is a straightforward and cost-effective solution. Forget the urban legend about the car recharging the key fob battery while driving – it’s simply not true! There’s no charging mechanism in these older BMW key fobs. This guide will walk you through the process of replacing the battery in your 2003 BMW 325i key fob, saving you time and money.
Tools You’ll Need
Before you begin, gather these tools:
- Vice-Grips: To securely hold the key.
- Paint Scraper: For initial prying to start opening the fob.
- Sharp Knife or Precision Blade: To carefully slice and separate the glued fob casing.
- Small Tipped Soldering Iron: For desoldering and soldering the battery leads.
- Silver Solder: For creating secure solder joints.
- Small Chisel or Pocketknife: To remove old battery leads.
- Wide Jaw Pliers (Channel-Locks): To hold the PCB steady.
- Rubber Band: To apply gentle pressure to the pliers.
- New Panasonic VL2020 Battery with or without leads: The correct replacement battery for your key fob.
- Plastic Glue: To re-seal the key fob casing.
- Clamps or Rubber Bands: To hold the fob closed while the glue dries.
Step-by-Step Battery Replacement
Let’s get started on replacing that battery and getting your 2003 BMW 325i key fob working like new again.
Opening the Key Fob Casing
The BMW key fob is designed to be securely closed, meaning it’s glued shut. Take your paint scraper and insert it into the end of the fob where the keyring attaches. Use the vice-grips to firmly hold the metal key portion. Carefully begin to slice along the seam of the fob casing with your sharp knife, using the paint scraper to gently pry it open as you go. Work slowly and patiently to avoid damaging the plastic.
Identifying the Battery
Once you’ve carefully separated the fob casing, you’ll see the internal components. The battery is located on one side of the printed circuit board (PCB). In the 2003 BMW 325i key fob, the original battery is a Panasonic VL 2020. It’s typically spot-welded with custom leads for connecting to the PCB. You can purchase replacement VL2020 batteries online. You might find options with pre-soldered leads, but as the original author notes, a plain battery and reusing the existing leads can sometimes be easier to work with.
Removing the Old Battery
Now, you need to remove the old battery. Use the wide jaw pliers to gently grip the PCB. Secure the pliers with a rubber band to maintain a light but firm hold – avoid squeezing too tightly and damaging the board. Apply heat from your soldering iron to the points on the back of the PCB where the battery leads are soldered. Once the solder melts, gently pull the old battery and its attached leads free. After removing the battery, use your chisel or knife to carefully detach the custom leads from the old battery. These leads will be reused for the new battery.
Soldering in the New Battery
Take your new VL2020 battery and the leads you removed from the old battery. Solder the negative lead (the one with the smaller pin) to the negative side of the new battery (the side without writing). Use a minimal amount of solder to ensure a good connection and maintain a slim profile for fitting back into the fob. Next, solder the negative lead back onto the PCB, making sure to insert the smaller pin into the correct hole. The battery should sit neatly within the white insulating pad on the PCB. Now, solder the positive lead to the positive side of the new battery and then to the PCB, again ensuring correct pin orientation.
Reassembling and Gluing the Fob
Before applying glue, test fit the fob halves together without the PCB to ensure a clean closure. Clean any frayed plastic edges from opening the fob to ensure a tight seal. Apply a thin bead of plastic glue to the perimeter of the fob casing. Carefully place the PCB back into one half of the fob, and then close the two halves together. Use clamps or rubber bands to firmly hold the fob closed while the glue dries completely, following the glue manufacturer’s recommended drying time.
Key Fob Resequencing
After the glue has dried and the fob is reassembled, you’ll need to re-sequence your key fobs to your 2003 BMW 325i. Follow these steps inside your car:
- Close all doors and ensure they are unlocked.
- Insert your first key into the ignition and turn it to position 2 (dash lights on, but engine not started).
- 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. The car’s central locking system should respond by locking and then unlocking the driver’s door, confirming successful sequencing.
- Repeat steps 2-6 for any additional key fobs you have.
Important Note: Any key fobs not re-sequenced during this process will not function correctly and will require you to repeat the entire re-sequencing procedure for all keys.
Conclusion
Congratulations! You’ve successfully replaced the battery in your 2003 BMW 325i key fob and re-sequenced it to your vehicle. This DIY repair saves you from expensive dealership costs and gets your key fob working perfectly again. Enjoy the convenience of a responsive key fob once more!
