Two perhaps related issues with my 2006 Mazda5

(1) A few years after we got the car we noticed intermittent problems where the remote locks wouldn't work using the key fob. one of the two keys was dropped and exploded, so we were left with one working remote key. Over the years that key is able to remotely open the locks less and less. I have changed the battery, but it made no difference. Now we are lucky if we can open the car remotely 10% of the time.

Any thoughts on what the problem might be and how fix it?

(2) Also a few years after having the car, I noticed that sometimes i couldn't make the internal lock switch unlock all of the door locks and back door. if you clicked on the Up side of the switch on the driver or passenger door, nothing would happen to the other door locks. This has become more and more pronounced, and now happens about 30% of the time. Because the remote lock rarely works, I usually have to manually open the driver side door and then use the internal switch to unlock the other doors. If that does not work, I can ALWAYS get the other doors to unlock by putting the key in the ignition (without turning it) and hitting the unlock switch again.

Why would that work but the regular method of unlocking the other doors not work?

 

Could be the ignition switch, Are you using original key or a copy? I had this problem with a Grand Am I had, My mechanic had to replace the ignition. I don't have a keyless entry on my 92 626. I notice the symptoms sometimes on this car.
JIm