So what actually went wrong? I haven’t opened the solenoid yet, but it was ONLY the solenoid that was bad. The starter motor ran fine, and technically the solenoid may have been fixable, but roomy wanted his car reliable for the winter so he opted to replace the starter with OEM ($$$ – way more than the $100 quoted in the guide). Not including (my) labor (tried to save him some bucks for the holidays), the 2022 costs for a battery and starter were north of $600! Granted, I’m sure you can do much better with a cheaper battery and an parts store starter, but your mileage may vary.
I have a feeling that the solenoid coil may have gotten burnt/shorted due to the old battery’s lack of juice – perhaps it tried to engage, and instead turned into heat. Hopefully I’ll take apart and post a follow up if I do. I guess take this as a word of caution; if you have a 2.4l Hyundai, don’t keep trying a dead battery!