I think you may need to be very careful with this one. Most cheaper units are modified sine wave output and in some cases this could damage the laptop. I think you may need to go with a PURE SINE WAVE inverter, they are more expensive but will give you a supply the same as household electric, smoother and more regular, the cheaper modified sine versions produce hard edge power that is ok for a light bulb or kettle but not for audio or more delicate things.
I ended up getting a pure sine generator to power my studio lighting outside, this is a very large item and not what you are looking for but I think if you do a google search for PURE SINE INVERTER you will fine a few around from about £65 up.