Sorry to resurrect an old thread but I have the same issue as the OP.

My key stopped working so I cut it open and replaced the battery with a new panasonic rechargeable.

It worked fine for nearly two weeks and then stopped working again. I have checked the voltage on the battery and it is down to 2.67 volts.

I'm pretty certain that the car is therefore not charging the battery.

Any ideas what could cause the inductive coil to stop working ? I guess the simplest option will be to replace the battery again with a normal cr2025 and leave it at that.

Thanks

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04 x5 3.0d sport