Assuming your laptop uses a typical transformer that converts your AC line voltage (110 or 220) that drops the voltage to the 19.5VDC that most laptop use, you could get an inverter that uses 12VDC input and outputs AC voltage (110 or 220, depending upon your location). Then plug your normal laptop transformer into the inverter. Not particularly efficient due to conversion losses, but then laptops do not use much power. Anything over 200W inverter should be more than sufficient for most laptops, but check the transformer on yours.
The inverter does not have to be a pure sine-wave to run a laptop.
Bryan