CD player stopped loading CD's but radio still worked. You could hear it trying to load a CD. Drove car for weeks this way.

I took the player out and cleaned/lubed everything. Worked one more time.

Then I had other weird things happen like the sat nav screen turn on and the radio display was all black, then went clear, didn't come on. Car drove normally.

Since that's a sign of a weak battery, I tested and found my two year old battery would not take a charge.

This time, got an AGM type, everything works again. I suspect the old one may have been the cause of other weird problems like sometimes having to press the unlock or lock remote buttons really hard to get them to work or the windows forgetting their settings. Finicky indeed about battery condition!

tl;dr: If CD player won't work, check the battery.