I had/have the same issue with our 2005. The service rep said the keys don't hold a battery charge for very long. I would do most of the driving using "my" key, programmed to my settings. My spouse would try to use her key after being idle for a month, and it would not work.

The rep said it takes a few hours to come up to full charge. This would also explain why a key starts to malfunction in mostly short trips for a long period of time. Seems odd to me, but that's the deal.

Dan

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Dan
2005 X3 3.0 White/Black/Aluminum