All conventionally purchased laptops should come complete with the battery and power "brick".
We've 3 laptops at home, all usually left on mains power, without apparent ill effect. Running on batteries to low power and then re-charging will prolong battery capacity and life though.
The heat issue isn't a problem unless your colleague wants to sit with it on his lap for hours on end (whether running on battery or mains) in which case he'll certainly have sweaty thighs.
Centrino laptops are usually optimised for maximising battery run time if that's an issue.