Libreoffice 5.2 is my current version but it happened on the previous version as well. When I open Libreoffice on my laptop the computer becomes quite warm and the battery drains within an hour. This does not happen with other programs. My only guess is that for some reason the GPU is being activate by Libreoffice and going 100%.
See this earlier question, libreoffice-using-dedicated-video-card-and-overheating-notebook
May be usefull for others if you could post which operating system and which GPU on your system.
Under the menu Tools, Options. In the LibreOffice, OpenCL option, are options to allow use of OpenCL which also uses the GPU of your graphics card.
You might also try latest driver updates for your GPU before disabling OpenCL.