My MPB retina mid 2014 is displaying peculiar behaviour. When I'm doing a long render in Adobe Premiere it seems to seem small amounts of battery from it, while being plugged in. After 1hr 30m render, the battery dropped down to from 100% to 95% and resumed charging after the render has finished. I had another display of this behaviour today during a 45 min render where the battery dropped to 98%. What demons are at play?