Highly caffeinated energy drinks do not do the same thing that sports drinks do for the body. Caffeine, and the other stimulants in energy drinks, supplies the body with a very strong and not very long-lasting energy boost. Sports drinks are designed to re-supply the body with carbohydrates, electrolytes and salts that they are using and losing while being active.
Also, energy drinks contain a very high amount of sugar, much higher than the levels found in sports drinks. This makes energy drinks unsuitable for rehydrating the body, while sports drinks do help supply the body with its needed fluids during vigorous activity.