[nayuki]

Correct. The parent of your post should have written "10 trillion kelvins", "10 terakelvins", or "10 TK". The article wrote "Temperatures there reach an astonishing 30,000-50,000 kelvin" instead of "kelvins" (or better yet, 30–50 kK).

Very few people use the unit kelvin correctly. ( https://www.reddit.com/r/Metric/comments/126sniq/everyone_mi... )

The only exception regarding capitalization is that the person Celsius is capitalized in the multi-word unit "degree(s) Celsius", and the pluralization is on "degree".

[hanche]

Good point about pluralization. I tend to be confused about that because we don't pluralize units in Norwegian (except the equivalent of degrees). But confusingly, in English, you sometimes see people trying to pluralize the abbreviations, such as kgs for kilograms. Or (even worse) ms for meters. That way madness lies.