What are the best Hardware for the lowest consuptiom on the HA

I already have an HA system at home and enjoy using it. However, my father wants to install one in his motorhome. Most of the recommendations I’ve found are for home users with access to power from the wall. Since it will run constantly and the motorhome’s battery will be limited, I would appreciate recommendations for computers that consume low power as much as possible.
Such as mini pcs, PIs or even ARM if possible (Not sure if it runs HAOS)

Additionally, do you know of any battery sensor readers compatible with HAOS? It would need to read the main battery power and disable anything when it drops below 30%.

Welcome! There is a thread in this forum where others have discussed this:

HA for RV or Marine Use.

And a popular link to another blog:

https://www.adventurousway.com/blog/running-home-assistant-rv.