[Migelito]

Fellas, I have to confirm the dirty contact extreme sensitivity.
Here is the story: my 535xi 2015 F10 car was showing low battery on the key. I replaced the one with a new CR2450. Tried to access the car and no luck, only through buttons. To start the car had to hold the key at the column, whose position was extremely sensitive to begin with. After reading what you all wrote, tried to give it a change: removed the new battery, wiped a few finger prints (!!!) with a cloth, wiped gently the "+" and "-" contacts inside the key, replaced the battery back and: the car now can sense the key, comfort entry works, car starts without the key at the column.

the lesson learned: be careful with the fingerprints, and just wipe gently the contacts inside, place the battery nice and firmly in against the contacts.