x300 way too hot when running on battery

[sputnik611]

Hi all - a quick question. I've noticed that when my x300 (with XP, 6 cell battery) is running on the battery (not plugged in), it gets super-hot on the back left side, where I believe the fan unit is. I can hear the fan faintly running. When I plug the computer back in, it seems to cool down a bit. Anyone have any advice? Aside from the computer being really uncomfortable to use, I'm afraid the excessive heat is going to damage it. thanks much.