Firstly laptops & netbooks don't have a common DC input voltage requirement. It varies from model to model between 12 to 24 volts...
Bottom line I wouldn't recommend doing that in anything other than emergency
Certainly. Check the AC adapter, it will tell you what the maximum output should be. I have not personally run across a 24 volt system, but that doesn't mean they don't exist ;-) (All Indians walk in single
file - at least the one I saw did...)
My analogy would be that running on unregulated 12V is like driving a car with the skinny little spare tire on - it gets you where you need to go but you don't want to push it. I did use 12V direct from the house battery bank to a Toshiba laptop on a seven week 6800 mile trip across the Pacific and did not suffer from any voltage spikes or low voltage conditions but I wouldn't intentionally set out that way. That passage
got me to get a Lind DC/DC converter - the high end stuff at $160 - but most laptop vendors carry a car adapter for their models at much less cost.