My Macbook Pro 15" unibody battery had went completely dead and I couldn't even power my laptop on when it was plugged in.
I was so glad that I bought the tools from iFixit along with the battery. The screwdrivers fit perfectly, and there were 3 Tri-wing screws that needed the special screwdriver, so it was great having everything I needed right away!
Get the battery and the tools needed here, that way you are not compromising or running to a store to get specialty tools that are tough to find. I hadn't even heard of a tri-wing screwdriver/screw before! The spduger was also nice because it is plastic and doesn't scratch anything that you pry on.