My Nikon 3100 Viewfinder is dark?

I charged the battery and put it in and now suddenly when I look through the viewfinder its is darker than normal but it still takes gorgeous pictures. Because not enough light is getting in it is difficult for it to auto focus. I changed the lens and the same thing happened so I know it is the camera body. It has not been dropped. Anyone know the problem?

Added (1). Ouch… Thanks for the snarky answer. I know the battery has nothing to do with what I see through the lens. It worked before I charged the battery and now it doesn't work. I have literally taken 10, 000+ pictures with this camera and know that what I'm seeing is different. The battery comment was simply to reconstruct any actions that led up to the problem. The viewfinder and the live view mode are both 60-70% darker than they normally are. I just wanted to see if this has happened to anyone else and what they did to fix the problem. Thank you for your opinion on my knowledge or lack thereof but that is not what is in question. However since you are of no help at all I shall ignore the snarkiness and see if anyone else can help!

The battery has NO affect on what you see through your viewfinder. How much light strikes the focusing screen has all to do with the amount of light in the scene.

You really need to learn some of the fundamentals of photography, because it is clear you do not understand them. What you are experiencing is part and parcel of using a fully adjustable camera.

This is true for ANY dSLR camera, not just yours.

In situations like yours, the first place I recommend for help is always the manufacturer.

In your case, I would call Nikon at 1-800-NIKON-UX (1-800-645-6689)

Go in to the menu's and perform a full, reset. It sounds to me as if you've been fiddling with the settings and altered the the manner in which the lens aperture closes down. Normally, the aperture is wide open until you press the shutter release fully down, at which time it closes down just before the shutter is fired. However it is possible to change this behaviour so that the aperture will close to reflect the camera setting immediately (ie without the shutter release being pressed).

I think there's something wrong with you camera.since you have taken more than 10K images. I will recommend you to consult with company or service centre before it get worsen.

Check that your depth-of-field preview isn't jammed and that the lens is mounted correctly.

The battery indeed has nothing to do with the viewfinder. Take off the batteries then look through the viewfinder. You should be able to see through it still. The viewfinder of a dSLR camera is optical. You also see through the lens itself. You actually see what the camera sees exactly. If it's darker now, then maybe it just got darker in your place. If you think we're giving you silly answers, the only way to verify your worries is to bring the camera to an authorized Nikon service center for proper diagnosis. I guess everyone especially you would agree to that.

Me? Nikon viewfinders were always dark for my taste. Have you happened to look through a Pentax viewfinder lately? In comparison to Nikon, Pentax viewfinders are the brightest you will ever see even on their entry-level cameras today, even during the film era way back when.

@fhotoace You are so rude. You really should learn some social skills.

^^^^^ Rude or not, those claiming the dark viewfinder has nothing to do with battery power are factually wrong. Yes, it's an optical viewfinder, but there's an LCD overlay that darkens the viewfinder when there's no power. Try removing the battery from a D5xxx series or D7xxx series and see what happens in the viewfinder. The owner's manual even mentions it.