This is the problem. I am an endurance athlete and I tried Rockstar but the sugar content just means spike, then crash, then crucially, you are more dehydrated

This is the problem. I am an endurance athlete and I tried Rockstar but the sugar content just means spike, then crash, then crucially, you are more dehydrated after drinking it than you were before! So you either realize this was a mistake and switch to water (and stick to Powerade in future which has the ideal sugar content for fast absorbing without the aforementioned problems) or chug another Rockstar... you can easily get through several 500ml cans that way. The MilFit/CrossFit group I train with now frequently issues warnings about no energy drinks before big workouts.