The longer you sweat while running the more electrolytes you lose. And the more electrolytes you lose the more your feel fatigued.
One solution for these problem is buying sports drinks that contain extra electrolytes but these sports drinks do not come cheap.
Researchers have found that the more salty drinks athletes consume, the less urine they produce and the fewer electrolytes they lose.
Home made endurance sports drink
Runners can make their own home made endurance sports drink by mixing water with salt and sugar. It is that simple. I got this idea from a magazine article about ultra marathon running. One runner said he drinks it to avoid stomach cramps. The mixture has a nasty taste but once you get used to it you will be fine.
I always drink a mixture of water plus sugar plus salt before I dash out for my long runs.
Just remember not all drinks work for everyone.