Batteries for a camera?

Hi

Does anyone know if there's such a thing that you can place under your DSLR and it gives you a lot more battery than the normal small batteries? I think that a few months ago I looked at something that looked like a big battery and it was places under the DSLR where you would normally connect to a tripod but i'm really not sure if it was that… If anyone knows what it's called or if anyone can correct me that would be great. I need it for this winter trip and i'm planning on making a film

I have a Nikon D90 if that helps

You can get generic portable packs mean for smart-phones or laptop computers. With those, you can likely get a cord to plug into the DC power in on the camera.

It's called a battery grip - they generally take two standard batteries and duplicate the right-hand controls.

Check the Nikon website to see if there's one available for the D90 (I honestly can't remember) and remember that you have to buy the batteries separately.