While on navigation watch the other night, I had hours staring into the darkness to think and started to wonder if your non-starting key was a replacement that was cut but not chipped/coded/synched to start your car.
The Diamond keys have coin batteries soldered inside. They can be replaced, but success is 50/50. They recharge whenever the key is in the ignition, but the car needs to be driven a while to recharge. Batteries do wear out, as do the circuit boards/button mechanisms.
Buy socks on Amazon, not car parts.