I was a little freaked out when I pulled my "spare" key out to start using and it did not work. I have kept the key in a drawer and pulled it to keep with me on MTTS. When it would not work I of course did an extensive search on the forums and learned how to reprogram the car as well as many other "things" which is why I love this forum.

I will admit, I was a little confused after all my reading. Does the key have a battery that needs to be replaced? Does the key charge in the ignition- which is what the dealer told me in 05 but I also failed to rotate the keys as advised.

I drove with the new key for 4 legs, each 45+ minutes (commute to and from work) and the remote still would not work. I was going to swing by an Advance Auto today on my way home to check the signal from the remote... well the 5th 45 minute drive seemed to do the trick, the remote worked when I left the car in parking garage.

So, at least in the 05, the key charges from the ignition. It took a lot longer than I thought, but it did charge.

Just my $0.02

 

With a 2005...
You use the key in your car...and it indicutivly charges....a few hours of driving will do it...rotate your keys every few months...
They are not made to be replaced...has been done with the right rechargeable battery...but hacking up the key is the usual outcome....a few threads....but remember, 2005+ keys are not made to have the battery changed like the earlier gen1 keys.....
So your olservastions would seem to be correct....
At some point the batteries WILL die and not accept a charge....THEN time for a new key and keep the old one as a spare or try to hack it up...