We need more details to recommended something to meet your needs.
- What are you photographing? Is it a large object/scene, or a smaller object/scene?
- How many hours on end do you expect the flash to run?
- How much light do you need the flash to output? A lot? A little? Is this light meant to be the main light for the photo or is it supplemental?
Running a flash for hours on end flashing 1-2 times per second can quickly overheat a flash, which can lead to problems. The lower the flash output, the better it will handle that heat and the longer it will be able to run.
But with that being said, depending on how many hours and how much light you need you might be better off with ac powered LED light panels instead of a flash.
You might be better off with an LED panel. Something like this, which can run off an ac adapter.
But as the other commenter mentioned, if this is running unattended for 6-8 hours safety is a big consideration. Be aware of the heat these lights will generate and the safety of the electrical cords and connections you plan to use.