All, my base 997.1 is treating me with messages lately when I start her. It's not driven much since March. Maybe once per week for ~20 miles. Just to keep the charge.
The car is complaining about the right front side marker (working just fine) and briefly gave me 'Tip in emergency mode' and today 'PSM in diagnostic mode'.
Drives fine, no CEL, no codes. Is that a sign of a dying battery?

 

sounds like the battery is getting tired. If it's older than 4 years, you're probably close to needing a new one anyway, so that would be my first step, assuming error codes don't obviously point to something else.

 

Sounds like battery to me too. For that type of limited use, yiu should be keeping it on a battery tender when parked to keep the battery topped up. Letting the battery run down and only driving it for 20 minutes is going to kill the recharge capacity of the battery.