Daniel,
I have other earbuds, like the Sennheiser momentum 2, that also use the right earbud, yet they don't have the same issue. Both earbuds are shown wrt battery life, so it isn't that the battery levels are masked somehow. I originally thought it might have to do with the codec used to process the sound. I haven't measured the battery life on my surface book 2 vs my iPhone. Perhaps I'll test that next.