You might want to double-check that one too. No-sugar-added fruit juice has a higher energy content per ml than coke, so not exactly ideal weight wise. Also, some of them are fairly acidic which is potentially an issue teeth wise. So best not to make a regular habit of it.
When you exercise sweat right & the sweat tastes slightly salty. Thats the salt the sports drink are trying to replace. Sugar you need for energy. They usually contain 2 other kinds of salt aside from tablesalt (NaCl) I think its potassium and magnesium not sure though.
I googled the difference between an electrolyte drink & isotonic drink and I see I was slightly off. Isotonic does mean salt & sugar just like the other electrolyte sports drinks....but it also means that the level theoretically match that in the body, so no osmosis should take place and it shouldn't be dangerous.