Do you need sports drinks and electrolytes?
For most people, most of the time, no. Electrolyte products are marketed far beyond the circumstances where they provide a benefit.
What electrolytes are. Minerals carrying an electrical charge in body fluids — principally sodium, potassium, chloride, magnesium and calcium — essential for nerve signalling, muscle contraction and fluid balance. Sweat contains them, sodium most abundantly.
Why ordinary exercise does not require replacement. For sessions under about 60–90 minutes at moderate intensity, water is sufficient, and a normal diet replaces what sweat removed. Most diets already contain more sodium than needed, so the body is not short of it. Losses from an hour's exercise are small relative to daily intake.
When they genuinely help:
Prolonged endurance exercise, beyond roughly 90 minutes to two hours, where both fluid and sodium losses accumulate.
Heavy sweating in heat and humidity, where losses are much larger.
Being a "salty sweater" — individual sweat sodium concentration varies several-fold, and visible salt residue on skin and clothing indicates high losses.
Repeated sessions in a day, or successive days of heavy training.
Illness with vomiting or diarrhoea, where oral rehydration solutions are genuinely valuable and are the clearest legitimate use.
The carbohydrate question is separate. Sports drinks contain sugar, and for endurance beyond about 90 minutes, carbohydrate intake genuinely improves performance by sparing glycogen. For a 30-minute gym session, that sugar is simply calories.
Hyponatremia — dangerously low blood sodium — is worth knowing about. It arises from drinking excessive plain water during prolonged exercise, diluting blood sodium, and has caused deaths in marathons. Guidance has moved from "drink as much as possible" to drinking to thirst, which is a reliable regulator for most people.
Practical summary: water for normal training; electrolytes for long, hot, or repeated efforts; and thirst is a better guide than a schedule.