Hi hi, just want to share my successful replacement of rechargeable battery of my R55 Key Fob. I have been using my car for more than 5 years and one of my key was out of juice few months ago. Though i put it back at the ignition key inserting place and drive for recharging the key fob, it was still malfunction.
I asked the BMW shop in HK and they said the key could not be repaired and it costs about HK$3500 for a new one including coding and engraving the key.
I tried to source the internet and strangely that no topic talking about how to repair the key fob (perhaps some for BMW which is more or less the same). Luckily I saw a topic "R56 Keyfob disassembled" which is somehow relevant and then I tried to fix it by myself.
Special Thanks to Millski
who gave my the guidance on how to remove the casing.
2. key fob ring (cuz the original plastic one must be damaged when taken down) (I had replaced a new metal ring for few years.
3. solder gun (no need soldering tin cuz the original one could be reused)
4. Panasonxx VL-2020 3V (180degree) rechargeable battery (can be bought from ebay or taobao) It costs not more than HK$50 for 1 pc.
5. glue (for reassembling)
1. remove the existing ring and the mechanical key
2. use a sharp cutter and insert it into the gap of the key fob and cut off the original glue carefully. as it is unavoidably making scratches on the key fob, so it is suggested to cut off the glue at the hidden part by the key fob ring (not at the engraved key side which is exposed)
3. after a while, the key fob will be separated like this.
4. bought a new battery from web or market. be sure it is 180degree (market has 90 degree).
5. Use a solder gun and carefully heat up the soldering tin of the footings of the existing battery and the battery will be dropped off. Remember don't heat up other parts of the electronic board.
6. use again the solder gun and carefully heat up the remained soldering tin on the terminal of the electronic board and insert the new battery into it.
7. Now, reassembling the key fob in reverse procedure. be careful that there are some small loosen parts, like the chrome button which is for releasing the mechanical key, the rubber for this chrome button.
8. glue the key fob. and reassemble the new key fob ring and mechanical key.
I tried the key with new battery for few days already and i can remote operate it in a further distance than my another 5-year key.