It's difficult to keep hydrated here.

I use those powdered electrolyte mixes. Brand names such as D-Champ, Oras, etc. They are sold in one serving envelopes that you mix with eight ounces of water. Since the brand names are in English but the ingredients are in Thai, it's difficult to know what is really in them and in what proportion. They are very sweet, so I know there is a large amount of sugar in them. I'm just wondering how much actual electrolytes (sodium and potassium salts) are in them?

Try the coconut water. (the green ones that they chop a square at the top and give you straw to drink out the water inside sold by many street vendors.

It is a natural electrolyte replacement and has many advantages over the manufactured stuff.

Google it.

I would say for a healthy adult, who is eating proper regular meals and drinking water regularly throughout the day especially durng hot weather, then these electrolyte mixes are unecessary.

However, if you have bad diarrhea, are a chronic alcoholic, miss meals regularly, exercise in hot weather and have other physical disease, then they are a good idea.

Eating and drinking water are the key here. Drink too much water and don't eat, you will flush away your electrolytes. Don't do it.

The packets you mention do indeed have the right stuff in them, but as others have mentioned so do green coconuts. As do the fresh fruit juices (nam minao, nam sam) sold here which the Thais typically add a dash of sugar to, making them a good electrolyte replacement.