I bought a used 2019 MINI four-door with 28k miles about a year ago. It has recently had an issue cranking up. There's no pattern to it. Sometimes it happens after the car has been sitting for a day or so, but there was another time, for example, when the car was unused for about six days, and it cranked right up effortlessly, like it was a brand-new car.

I don't think it's the spark plugs and the battery is still good. Is it likely to be the coils? Before this car, I had a 2013 MINI hatch, a model that came with factory ignition coils that were infamously garbage. Do the third-generation Coopers also come with crappy ignition coils? Or is the long cranking the symptom of something else?

 

If your measure of the battery still being good is that it has 12.5V at the battery posts using a multimeter, that doesn't tell you everything you need to know. The F series MINI uses an AGM battery -- for an AGM, State of Health (SoH) -- which a multimeter won't tell you -- is the measure of consequence (and decidedly nonintuitive to interpret even when you have that info).

If you have a scanner or other tool capable of showing you SoH then the upshot is that anything in the low 80%s (or less) is not great and life can get interesting on the F series MINI (including symptoms that are intermittent and nonintuitive). If you don't have such a scanner, old school load testing can tell the tale, but that's a pain in the neck / you have to find a place to do it that actually knows what it's doing / etc.

Shortest version: you can have proper voltage at the posts, but the battery may not be holding a charge well and/or it may dive too much too fast when substantial load (starting crank) is put on it.

I know this doesn't give a firm answer, but if the issue is basic electrical, this would be the starting point. And it's more likely than bad coils, especially if the car (and therefore the coils, presumably) have a mere 28K miles on them. Coils are possible but it's not first guess by a long shot.

 

One indicator of my battery dying on my F56 is that the windows don't roll back up all the way after opening and closing the door.