Belkin makes an excellent portable fan/tray gadget that's perfect not only for keeping your laptop at room temperature but also for elevating the keyboard for better ergonomics if you're fortunate enough to have a table to stick your laptop on. It plugs right into the computer's USB port and draws a minimal amount of power.

If heat is the enemy of battery life, getting a good quiet cooling fan will save your bacon and your bucks. You can find Belkin's model for as low as $20 on Amazon (search "Belkin laptop fan" and shop 'til you drop.)

(disclosure: Belkin isn't paying me or in any way responsible for this endorsement; opinions are strictly those of this post's author.)

The problem with USB powered fans (or USB-powered anything) is that they suck power off the battery - so the battery life is actually less than not using one. (But it does life the laptop enough to make the laptop's fan a bit more useful....) Also, the laptop fan removes heat from mainly the processor, not the battery - airflow is usually routed over the main circuit board, not the battery.

All of the above is certainly true, but when I lift up my laptop and touch the entire underside of the housing, the battery's as cool as everything else on the computer (Toshiba does a great job of putting the components in such a way as to maximize the effectiveness of the fan underneath it.)

Short-term, that USB fan is draining the battery, but long-term, keeping the laptop cool (if it's well-laid out as described) is going to lengthen that battery's life.