240v Inverter For Laptop

[V8RX7]

I'm running an old laptop with a serial port to tune my MX5.

I was using an old 150w inverter but it kept beeping "insufficient power" then the laptop battery died.

The laptop's own battery works for 30mins and it seems uses max 150w so I presume it meant there was insufficient power from the car ?

But as the car can happily run everything it uses I can't see that's correct.

Is it just a case of buying a new inverter in which case should a 150W be sufficient or do I need to overspec it ?

[V8RX7]

Hmmm I have a large boost pack which is obviously 12v

I see there are things like this:

http://www.ebay.co.uk/itm/Car-CHARGER-for-Dell-Lat...

But I thought DC DC couldn't step up