I left one day, drove about 20 miles to a meeting at my daughter school that lasted about 10 minutes, I came out and my car wouldn't turn over at all. I thought maybe I had left the lights on and run the battery dead, so I called my dad. About 10 minutes before he got there I tried to start it, and it turned over and started just fine. Then I had a doctor's appointment about 20 miles away, I was in there for 5 minutes, and same problem -- wouldn't start. Called my dad again, and 2 hours later he got there and started it right up. I drove it home that afternoon, and I checked to see if it would start and it did but it hasn't started since. If you could help me it would be unimaginably appreciated thank you have a nice day Krystal!
You need to do what is called a "voltage drop test" on the battery and starter cables, both positive and ground.
If the cables have become corroded, they will not flow sufficient current when hot. Only when they hsave cooled off will they provide enough current for a start.
Also the starter solenoid may be experiencing the same problems. Check the cables, and if the cables check out replace the starter/solenoid combination.
An easy check is to put a voltmeter across the battery terminals when cranking (during a "no-start" episode). If there is no change in battery voltage, this is indicative of a failing solenoid.
Some solenoids can be replaced apart from the starter, but for a Hyundai it makes more sense to replace the entire starter assembly.
Also, your battery voltage while "off" should be at least 12.5 volts, checked by a meter. A third (least likely scenario) is the battery has a lead terminal runner that is seperating while hot. In this case, nothing would work - no headlights, radio, or any other electrical accesory.
I would start by checking the condition (electrically) of the cables.
I just fixed a 2012 Santa Fe that would not turn over, was happening intermittingly but then finally wouldn't do anything . All lights came on. Alarm was just about impossible to shut off. Ended up being a factory installed remote starter that the new owners didn't know was even in the car. This was after having the battery checked and taking the starter out and having that tested.