97 eclipse car problem

I have a 97 eclipse , I have had an alt. installed and about 8 new batteries and new cables. The car won’t stay running for more then 3 weeks or less. Nothing is ever left on in the car. What can be wrong with the car?

Bad grounds, bad battery cable connections, faulty alternator, etc.

Have a full (in vehicle) load test performed on the charging system.

Also, “what’s wrong” is, you haven’t found a mechanic, yet. If you had, you wouldn’t be on battery #8.
Ask around, even from “mechanics”, of someone who is capable of automotive electrical repair. There may be an automotive electrical repair specialty shop in your area.
Sometimes, lights or fans may come on after the car car should be asleep. A half hour after the car has been shut off, go to the car and listen for fans, or electric motors, or lights on. If you see, or hear, anything, tell your electrician/mechanic.

I had 2 alts. put in the car the first was defective. I have had a diagonstis test done and electrical test done

I have taken the car back to pep boys they put in the alt. and all the batteries and cables , nothing is running after the car is off. Also had an electrial test done on the car.