I did a

but could find no answer to this question...
I have a P4M laptop with a 16V 4.5A power source and I can find various power adapters that are suitable for it's use in a car straight from a cigarette lighter.
I am wondering are there any downsides to using one of these devices - for example - is the power it delivers well regulated? Does anyone have any favourite brands? Does it wreck the laptop battery?
Any help would be greatly appreciated!
Thanks!