Are third party batteries bad?

I'm getting a Nikon D3100 and need a spare battery. I want to pick up a Vivitar Battery (third party). I'm getting it because it is cheap. I'm just scared, if I use it, will it break my camera? I don't care about battery shortage, I just need something for those last hour of shoots. I just am worried about the camera. I'm getting a VIvitar En-El14 battery. I'm worried about camera, please inform me. I just need to know if it will damage my camera, I don't care about the life.

It won't damage your camera, if you still worry about it, use outside charging