In the OED, of the six senses distinguished, the thing measured by joules is in last place and dates from 1807. So it isn’t even a metaphor here.
If by “metaphor” you mean “using a word with a sense other than the historically oldest one, then whenever you’re talking about checking something when not playing chess you’re using a metaphor.
If by “metaphor” you mean “using a word with a sense other than the historically oldest one, then whenever you’re talking about checking something when not playing chess you’re using a metaphor.