The battery has only limited power and the electric motor is a high-performance model that draws quite a lot of current. That's why it runs out quickly. Actually quite simple.
I don't have the part myself, but go to the product again and then scroll down. At the bottom there is the accessories tab, which has RC car spare parts as a sub-tab. It says something about shock absorbers, but I'm not sure if that's the right one. :)