Electrical Power for Laptops

I just revived an old non-working laptop that we were given. What options
are available to get some added work hours out of it when away from the
house?

We have an inverter/drive corrector, and could plug that into one of our
17AH 12volt batteries, and then plug the laptop's AC adapter into the
inverter. That seems inefficient, and maybe there is a good reason not to
power the laptop this way.

Would it be reasonable to make an adapter to plug the laptop directly into
the 17AH battery, or is there some reason this would be bad for the laptop?

Thanks.

Clear skies, Alan