Mike,
I’d take David’s advice and change the battery, even though it has no problem cranking the engine. My guess is that the stop-start system increases battery degradation, leading to all sorts of seemingly unrelated electrical issues. The battery needs to be in tip-top condition, and if you can, invest in and use a battery conditioner regularly.
The online battery providers will be able to guide you in your choice, but Bosch and Varta are recognised quality brands offering good guarantees. As David has said the system needs to be reprogrammed to recognise that a new battery has been fitted and this can be done by a Porsche dealer or a reliable Porsche Independent with Porsche-compatible diagnostics, although it’s possible to purchase relatively cheap OBD2 diagnostic analysers which will do the job plus other things.
Jeff