Here is what I found in the 996 owner's manual ...

The remote-control standby function
switches off after 5 days, If the vehicle is not started or unlocked with the remote control within five days, the remote control standby function is switched off (to prevent discharging of the vehicle battery).
1. In this case, unlock the driver's door with the key at the door lock.
Leave the door closed in order to prevent the alarm system from being triggered.
2. Press button 1 on the remote control.
The remote control is now activated again.