Electrolytes…What Are They And What Do They Do?
(according to wikipedia)

Sports drinks
Electrolytes are commonly found in sports drinks. In oral rehydration therapy, electrolyte drinks containing sodium and potassium salts replenish the body’s water and electrolyte levels after dehydration caused by exercise, diaphoresis, diarrhea, vomiting or starvation. Giving pure water to such a person is not the best way to restore fluid levels because it dilutes the salts inside the body’s cells and interferes with their chemical functions. This can lead to water intoxication.

Sports drinks such as Gatorade, Powerade, or Lucozade are electrolyte drinks with large amounts of added carbohydrates, such as glucose, to provide energy. The drinks commonly sold to the public are isotonic (with osmolality close to that of blood), with hypotonic (with a lower osmolality) and hypertonic (with a higher osmolality) varieties available to athletes, depending on their nutritional needs
It is really not necessary to replace losses of sodium, potassium and other electrolytes during exercise since it is unlikely that a significant depletion the body’s stores of these minerals will occur during normal training. However, in extreme exercising conditions over 5 or 6 hours (an Ironman or ultramarathon, for example) the consumption of a complex sports drink with electrolytes is recommended. Athletes who do not consume electrolytes under these conditions risk overhydration (or hyponatremia).

Because sports drinks typically contain very high levels of sugar, they are not recommended for regular use by children. Rather, specially-formulated pediatric electrolyte solutions are recommended. Sports drinks are also not appropriate for replacing the fluid lost during diarrhea. The role of sports drinks is to inhibit electrolyte loss but are insufficient to restore balance once it occurs. Medicinal rehydration sachets and drinks are available to replace the key electrolyte ions lost. Dentists recommend that regular consumers of sports drinks observe precautions against tooth decay.

Electrolyte and sports drinks can be home-made by using the correct proportions of sugar, salt and water.

“What are electrolytes?”. February 05, 2001 http://health.howstuffworks.comquestion565.htm (September 25, 2007)

What are electrolytes?

Electrolyte is a “medical/scientific” term for salts, specifically ions. The term electrolyte means that this ion is electrically-charged and moves to either a negative (cathode) or positive (anode) electrode:

ions that move to the cathode (cations) are positively charged
ions that move to the anode (anions) are negatively charged

For example, your body fluids — blood, plasma, interstitial fluid (fluid between cells) — are like seawater and have a high concentration of sodium chloride (table salt, or NaCl). The electrolytes in sodium chloride are:
sodium ion (Na+) – cation
chloride ion (Cl-) – anion
As for your body, the major electrolytes are as follows:
sodium (Na+)
potassium (K+)
chloride (Cl-)
calcium (Ca2+)
magnesium (Mg2+)
bicarbonate (HCO3-)
phosphate (PO42-)
sulfate (SO42-)

Electrolytes are important because they are what your cells (especially nerve, heart, muscle) use to maintain voltages across their cell membranes and to carry electrical impulses (nerve impulses, muscle contractions) across themselves and to other cells. Your kidneys work to keep the electrolyte concentrations in your blood constant despite changes in your body. For example, when you exercise heavily, you lose electrolytes in your sweat, particularly sodium and potassium. These electrolytes must be replaced to keep the electrolyte concentrations of your body fluids constant. So, many sports drinks have sodium chloride or potassium chloride added to them.

They also have sugar and flavorings to provide your body with extra energy and to make the drink taste better.

Another example where electrolyte drinks are important is when infants/children have chronic vomiting or diarrhea, perhaps due to intestinal flu viruses. When children vomit or have diarrhea, they lose electrolytes. Again, these electrolytes and the fluids must be replaced to prevent dehydration and seizures. Therefore, drinks such as Pedialyte have sodium and potassium in them like the sports drinks do. However, pediatricians do not recommend giving sports drinks to a sick child! Sports drinks have much higher sugar concentrations than Pedialyte and the high sugar is not a proper treatment.

This is for your information only, please always consult your professional for professional advice!