I would recommend that you buy a 12v dc adapter to power your laptop.
Inverters are very power hungry. Take a look at these items at Maplins.
One of them is sure to power your lappy!T:
What is your lappy manufacturer/model?
seems a power hungry way of doing things using a mains inverter to bring 12 volts up to 240 volts - then the laptop mains lead transformer to bring it back down to 19v but if the inverter was free then fair play! if it eats your battery too much maplins do selectable voltage power supplies especially for laptops for around £20
How did the inverter work out? I am looking to make the same buying decision and am looking at both routes.
In favour of the DC-DC converter: Cheaper, more efficient as only one voltage conversion.
In favour of the mains inverter: Can use it with other things. Still uses the laptop mains adapter, which I trust more than a cheap DC-DC converter. If the cheap DC-DC converter fails and puts out too many volts to the laptop then it's Bugg888d. If the mains adapter that comes with the laptop sticks out too many volts then the laptop is still just as much Bxxd but I will have a better claim against the laptop manufacturer.
I've got a 600w inverter mounted in my van, to provide 240v AC to 2 twin 13a sockets.
It's been in over a year now & I haven't used it yet. Still, it is a good thing to have, just in case I do need it at some point.
If you can get a 12v adapter for your lappy (better if your manufacturer does one) I would recommend this. Makes your leisure battery last longer!