Sorry, but Ive tried to search with now results. I recently purchased a 2006 M35 and had to replace the battery in the key fob. Since doing so, the key fob isnt being recognized by the car. Do I have to pair it to the car again?

Unless there are differences between the model years I shouldn't think battery replacement will cause issues. I have an 07 and have replaced batteries in both smart keys with no issues.

Sometimes it does that, which sucks. Usually it will not lose its paired memory. I have a feeling there is some capacitor inside to store a tiny charge to keep its memory while there is no battery for a short time and most likely you took too long with the battery out and this charge didint hold long enough. What really sucks is that I remember another person or two that this happened to and the dealership charged something like $100 to do the reprogramming. Hopefully this wont be the case for you, especially if you just bought the car not long ago as the battery would be about dying anyway. But I too have replaced the battery a few times with no issues.

Thanks for the input... Does it make any sense that it is working sometimes. Since the first post Ive been playing with it and it seems like once in a while, usually after I put the key in the port to start it, it will work long enough for me to start it 1 time then right back to saying NO KEY

Perhaps the battery isnt in well enough then? Or the new battery is really old and losing its charge too?

I heard that they keyfob charges itself when plugged into the port (near steering wheel). Is this true?

I also heard that. However, it's not true. The key slot is there soley to be used when your smart key has gone dead, OR can no longer transmit codes to the car - the slot reads the code direct from the smart key instead of receiving code remotely.

If I were you, Van, I'd follow Enigma's advise - buy another battery - check the manual for ther correct model# battery needed and stay with a quality brand like Duracel instead of a store-brand copy. After you have tried TWO different batteries and still can't get the smart key to communicate with the car remotely, I would search for a local locksmith who specializes in programming smart keys. That would probably be less expensive than having the dealer do it.

I guess that battery display shows how much life there is left on the battery, I always thought it was telling me to plug the keyfob to charge LOL what a dummy! I've only had my M since March, still learning...
Locksmith maybe cheaper than Dealers, I bought a key off Ebay and had the dealer program/cut for $65.00 which is not bad....
got a free car inspection and carwash as well :-)

Thanks all for your advise. I'm going to try the new battery approach first after calling a dealer and getting told for just $250 they can fix me right up . Will post my results

They told me the same thing $200 for the Keyfob + Key and $65.00 program (total $265.00) as I mention I got one off Ebay for $68.00 and paid dealer to program it.
See thread below if you are going to buy a new one
smart-key-programming-t575380.html

Ikeys do not "forget" what car they are paired to. It is the car that remembers which Ikey can open it. As a matter of fact, one Ikey can open multiple cars. Each ikey is really an RFID device that also uses a battery to help transmit the code over greater distances.

As others have said, the slot is an RFID reader only and doesn't charge the Ikey.

It is possible that the body control module (BCM) in the car has failed, but this rarely happens.

The easiest solution is to try the other ikey and see if you have the same problem. If for whatever reason you only received 1 ikey; change the battery. I recommend buying it from a reputable store that turns over its inventory often.

Note: Ikeys last longer if you do not use the buttons on the Ikey and instead use the lock/unlock buttons on the cars door handles.