Nikon don't make one for the D50, so you're limited to 3rd-party add-ons like the following one:
Please note: I am not endorsing this product, it was the first one I found when I searched.
Having dismissed battery grips as non-essential for years, when I finally went for one for my D200, I was amazed how much better it makes the whole camera feel. All in all, with large lenses on, the whole setup is much more balanced. The extended shooting capabilities with two batteries is just an added bonus. The only obvious down-side is the additional weight! However, I liked it so much I bought one for my second D200.
Time flies like an arrow. Fruit flies like a banana!