If the battery voltage drops that fast then it is likely has a bad cell and is defective.
As you are able to jump start it and it runs fine the starter or the solenoid is not the issue. If it was the starter it would not have started regardless of jump start or not.
Perform a load test on the battery. This can determine if the battery is faulty.
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Tuesday, August 31st, 2021 AT 12:03 PM