What's wrong with my beater? 2001 Saab 9-5. Turbocharged 3.0

Was driving it like a month ago and the battery light came on, about 5 mins later the car felt like it lost a lot of power and eventually I had it floored and it would barely move. All the lights on the dash came on and then the car completely died. Battery was dead too, couldn't even put the windows up. Took it to a shop and told him I think I needs an alternator. He said he tested the battery and alternator and they both tested good but the check engine light was on and both O2 sensors were bad and needed replaced. Car was at shop for 2.5 weeks, he said he replaced the O2 sensors and the car would start up and idle fine and he even drove it 50 miles with no problems. I payed an assload of money for brakes, inspection stickers, sensors and labor. Drove the car home. Took it to work the next day and it seemed fine til the battery light came on on my way home. Next day driving to work and the same shit happens, light comes on and loses power then completely dies and I tow it home. WTF. Its been sitting in my driveway for a week. I'm trying to just get it running so I can trade it in.