Keyless entry not working sometimes...

[f5fstop]

I would guess it is not the battery, if it fails to work and thirty minutes later it works. Rest assured, Dephi filed bankruptcy after your delivery. However, I have bought brand new batteries to only have one fail immediately.
If it ever fails, and you have the other remote with you, try that before entering the vehicle. If the other remote works, there could be a faulty solder joint or circuit board in the non-working remote.
If they both don't work, take it to the dealer and see if a code has set. Could be a bad connection in the body of the vehicle.
Also, since the BCM is the receiver, the range of the remote is farther when you are approaching the right front of the vehicle.
RF interference can cause this problem; however, if it was due to large antennas, it would not have locked the doors in the lot. (Unless the NSA is playing around in your neighborhood. )
Whatever you do, do not push the remote 256 times without being in range of the BCM. If you do this, the BCM will not recognize the remote, since it will have passed the set point for the rolling code technology.