Interesting re: the "recharge" idea, sounds pretty sophisticated (and therefore, totally Porsche!?!).
I've not had any trouble with my keys, but they're still young yet at ~1 year. The only issue I've run into is what they tell you in the manual - if you don't start the car for several days, then you need to physically put the key in the lock to open the car. Then you're OK for remote use until the next battery saver timeout.
Now, if only I could aim the key a little better in the dark... and avoid those annoying little door keyhole scratches!