Most people realize electrolyte replacement is important, but fail to realize how much damage an imbalance can cause in an ultra. Runners with an electrolyte imbalance can lose many of their motor skills and become disoriented. Electrolytes are essential to the function of all living cells within the body. In an ultra, this can result in a loss of 20 to 40 grams. The consequences of failing to replace these electrolytes are extremely high.
Energy drinks contain some amount of electrolyte.
It's best to compare and choose one that supplies more than one that supplies little. Even these drinks cannot supply the total requirement. Foods such as crackers and pretzels which are readily available at most runs, contain some salt, but too little to really add up to much. The need for salt at aid stations in ultras is high, especially in 100-mile runs. Always check to see if the race will have salt available.