Can they run continuously ?
What is the DC input range on the high end for that?
Seeing alternators may get to almost 15vdc, It must be at least that high.

 

Yes they can be powered continuously and since they are designed for automotive use; they will be ok with the typical automotive voltage range.

 

The 40amp refers to the contacts, they probably won't last too long with a 40amp Inductive load, Resistive, maybe.
Max.

 

While they are fairly standardized.. They are not all created equal..
The best answer to your question is to "read the datasheet"...(RTFDS)