Using my laptop at a coffee shop today I was dismayed to find my battery down to 85% after just 15 minutes. The culprit seems to be that MATLAB's idle IDE was keeping my CPU busy (6-15%) and the bug is well known. The fix was to issue:
com.mathworks.mlwidgets.html.HtmlComponentFactory.setDefaultType('HTMLRENDERER');
and restart matlab. Now it's down to around 1% idle CPU usage.