I only have 600 miles on my Bolt, but my 2014 Volt did have one under warranty repair.
Some sort of sealed metal box containing what the tech described as the 12V battery charging system as well as a stepper that brought charging voltage from the wall down to 14 V or so, PLUS some guts that allowed the 12V computer components to safely interact with traction battery components.
It failed and my 12 V battery threw a low voltage error. With the added bonus of a continual angry bees plus growling cats sound coming from the rear cargo area.
This happened at ~7000 miles.
The only non cosmetic repair the car has ever needed, 100 percent covered by the basic warranty and or the drive train / voltec warranty.
Before that I had a GTI, which had a high pressure fuel pump go out at 15000 miles, and had a recall for the DSG gearbox, which was replaced entirely under warranty at 40K. 10 thousand before the basic covers everything warranty, and well before the ~80k drive train warranty, which would have covered that.
Before THAT, I had a Nissan Maxima, which had an HVAC part that controls where air flows to go out. At 20 K miles. Covered under basic.
Before THAT, I had an Acura RSX. The passenger side seat harness shorted out, disabling the air bag on that side. Replaced under warranty at about 1000 miles.
See the pattern here?
I tend to hold onto cars until at least 120 K miles. My Volt has been the exception which I am going to give to my neighbor / best friend, who has had a lot of horrible financial trouble lately. It has 78 K miles.