troubleshooting – Is my DSLR viewfinder dark because there’s no battery in the camera?

I’m new to DSLR cameras; as I love photography, I decided to get a Nikon D7500 with 18-140mm kit lens.

I’ve just mounted the lens to the camera but when I see through the viewfinder, the image doesn’t look bright and seems like the lens or the sensor is dirty, I already checked the camera and lens they are brand new. I haven’t put battery yet, could someone please tell me if this is a problem or just because I haven’t inserted a battery yet?