T42 battery power and fan question

[rocketman]

It's the first time I'm using my T42 on battery power, I have the 9 cell battery and the ultrabay slim battery installed. The fan seems to be on continuously, it's not loud by any means but in a very quiet room I'm conscious the fan is running. Is it normal for the fan to be on so much while on battery power? When I'm running off the AC the fan comes on just once in a while.

[itzmheck]

Same thing happens on my new t42p, I think its to keep the battery cool while using it. I heard LI-ION batteries then to get warm when you use them.