well i have noticed in the last couple of days that my twister does not do good in the grass anymore. i am thinking it is my battery. i put the same battery in my bandit and i got the same result. could this be the issue?

well, if the battery is not performing well in the bandit either then it sounds like maybe its not charging right anymore.
sometimes, a single cell of the pack will go bad...or the connections between cells. when this happens, the battery can no longer provide its full voltage or amperage.

also, what is the condition of the deans plug? a bad plug or a bad connection there will hurt performance.

its a traxxas plug. do you mean the strips of metal that the connection is made with?

well there is some blackness on the strips. could that be it?