RAM consumption does not heat up a computer at all. It's all about CPU load. So no matter how much RAM is full, your Mac won't get hotter. But naturley when there is much in the RAM there is also much to do for the CPU. The CPU gets warm under load and that's when the fans run faster.
But this does not in any way harm the battery. Parallels Desktop is still "software", even if it runs cosely integrated with OSX, will never and technically can not harm your hardware.
The batterie can however die and this is nothing to really worry about, Apple will replace it even free or for a charge. Nothing to worry about if you have a backup.
It's the same as with harddrives, they can also fail without any software to blame.
Last edited: Nov 22, 2012