2008MY with Comfort Access.

My daily key works fine. The secondary key, which I haven't used in 6+ months, does not have any remote function. It will start the car if it's in the slot, but the lock/unlock buttons do not work.

I have replaced the battery.

Is there a way to reinitialize this key?

 

I'm pretty sure you have to drive around with the key to let it charge for a bit. After not using for that long its natural that theres no charge in it. Use it for a few days, should be just like your daily key!

 

If he has replaced the battery then it is CA key and doesn't require car charging. I can suggest though that not all new batteries you put in are good. I would try yet another. I don't think its a problem with the diversity antennae as you state the first key works fine. There isn't any reinitializing as far as I know. It is hard coded to your car via VIN. This is why you don't find just anyone selling legit keys.