Beating a dead horse but I've searched here on the forum and now I am having the 'no key warning' issue on our 2009 Mini Cooper S. Wife parked it in the driveway (thank goodness it didn't happen somewhere else) and she came back out and got the 'slash thru the key' warning on the screen.
New battery in car in 2023 and it is fully charged via our trickle charger. Fob opens doors and does everything it's supposed to do but when inserted into the dock now we don't even get the slash through the key symbol. Just nothing at all. Fob buttons still open locks and locks door and opens hatch lock. Used Mini only came with one fob.
So... do we need a new fob from a dealer? And if so, which dealer? Are all the dealers going to charge the same? (we are 5 hours from nearest dealer)
thanks!

 

The issue could be either the immobilizer chip or battery in the fob or the CAS control unit that recognizes the immobilizer signal from the fob. I don't think the problem is the fob antenna in the rear view mirror because the fob works on the locks.

It may be worth calling some locksmiths.

 

@Mr. J ,

Did you re-register your new battery with your OBDII scan tool? You need to do that if you have a square box on your negative battery cable(IBS….intelligent battery system)

 

It’s been running fine since April of 2023 when I installed the battery. Would the problem just now be occurring?

 

@Mr. J ,

Your battery system can work fine for awhile before it starts acting weird. Did you check the negative cable for that square box?

 

Without the trickle charger connected, what voltage do you read across the two battery posts? If battery voltage is good, then watching these three videos may help...
https://youtu.be/JAv0916FDKg?si=hP8mccP5tLpW0I1T
https://youtu.be/GbdCaBKE7Kk?si=JM5hp6B9RvLlFEm2