Saab goes out 🙁

Hi, I’m new here and have been having a problem with my car for 1 week. Maybe someone can help with it. Problem: In the morning he starts without problems, drives me for 5 minutes to go out at the red traffic light and not to muck anymore. If you let him stand for about 20 minutes he jumps again without any problems and then drives as if there had never been anything. If I start again in the afternoon I have no problems at all. Urachen: My colleagues now have great ideas about what it can be nte: 1) Be a problem of an old battery? I tested in the stand today what happens when you turn on everything gradually. The result was: motor on – everything else off -> everything good motor on + ventilation to 1 -> twitches from time to time motor on + ventilation+light -> engine twitches more motor on + ventilation to 3+light+radio -> engine twitches and goes off. So– does this point to an age-weak battery? For more information, I bought the car 3 years ago and since then the battery 2) Frozen water in the exhaust 3) Defects Cold start automatic 4) Dirty air filter I would be very grateful about answers