12V to 20vat200w 8.5a how can i do it?

Hi.

I am very new to 12v systwms and know little atm altho a fast learner.

I have to power a laptop in old and powerful one used for photo editing..

The mains transformer runs at 170w 20v 8.5a i need to power this unit whilst out in the middle of the countryside for hours at a time.. I have 4 leasure batteries charged if solar panels. All good so far.

I am asking advice on how can i get from 12 v to 20v 170w 8.5a without using an inverter. I cannot afford a pure sine wave. And modified fries my mains power suppply.. And its also very poor efficiency to use inverter.

I found step up transformers but they jump to 24v.. 245w 10a.

Regards
Luke.