Not sure about keeping the blower on. I once ate lunch in my old car with the blower on for about an hour. Went to start the car after work and the battery didn't have enough juice.Your car can do that just fine - we used to do that with our Jeep for 3-4 hours before we got outdoor patio speakers. And you can probably run the blower on fan speed 1 or 2 without the AC on, if that will keep you cool enough.
The dash INFO display has a battery voltage meter. Keep an eye on it; don't let the voltage drop below 11.8 and you should be fine to start up the car.
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