Did my key battery die?
 

Drove the X5 with the spare key this weekend and found that it won't lock or unlock the doors or open the tailgate with the buttons on the key. Did the lack of use of the spare key kill the battery? Do I need to get it reprogrammed?

It usually takes about one year of non use for a fully charged key to lose power, so it can be good to take the spare one for highway trips every so often just to help maintain charge.

It takes a total of 30 hours in the ignition with the key on to fully charge a dead key, but only about 45 minutes of driving to regain the keyless functions (for a while at least)

If you have a good battery charger with a 30 amp output and a secure parking place like a garage, you could leave the key in and on overnight to put a decent charge on it.

hey weasel, i drive and hour to and from work every day. plus plenty of trips here and there during the day, but sometimes i have to press the unlock or lock button on my key a few times before it actually opens or locks. today i was outside the bank and i was standing on the passengers side and it took about a minute before the doors would unlock. whats up with that? i dont get it. do i need a new key? or a battery?....thanks

Wouldn't be able to know off hand what the weak link is... The battery in the key is not serviceable. I'd try another key if you have one to see if it acts right or if it acts up as well. (pending you having another full function key)

Sorry, I don't quite follow. What is the battery charger for? Couldn't I just leave the key in the ignition? Or does the car have to be on?

The key has to be on for the EWS tordial coil to switch over from antenna that reads to power output that induces voltage to charge the key. So the charger would be to keep the battery from dying as the key being left on otherwise would kill the battery all too quick.

Got it. Thank you.

I have the same issue with my key. I tried using the key for days but I cant even reprogram it to the car at all. Besides the battery losing its charge I dont understand how a sealed key can go bad when it hasn't been tampered with or abused.

I'm getting close to opening the key to at least check the voltage at the battery....

I understand that the wirelss encrytion on the key is quite sophisticated and that it uses a rolling code sequence based on an algorithm.

What this means is that every time you press the unlock button it sends out a different code. The receiver in the car uses the algorithm to decide if the code is the next one along in the sequence, and if so grants you access.

If you have pressed the key a few times when out of range of the receiver, the code will be out of sequence. To combat this the receiver always checks to see if the code is within a few moves of the correct code as determined by the algorithm, and if so, will still grant access. Where there can be a delay is if the unlock button is pressed repeatedly, whilst out of range, such that the code generated is too many moves away from the current expected code. What happens then is that the receiver then has to then compare the code produced from several sequential button presses to ensure that they are generated by the correct algotythm, if this is the case then access is granted after a few attempts.

I offer this as an explanaition of the delay that you sometimes experience when you come back to the car and it does not open after the first key press.

How the system recovers from a completely flat battery in the key I don't really know...

Sometimes the car does not open due to high electromagnitic field surrounding the area where you're parked. It always happens to me in places that I know, usually next to military bases where jammers are installed... does it alawys happen in the same place?