Formula for Homemade sports drinks
Maltodextrin.  It is basically pure glucose, which is the only sugar that your muscles can use directly without converting, so it's just pure energy.  It also has no flavor or sweetness, so it is completely inoffensive, and you can sweeten (or not) to your desired level. Look in any sport beverage and it will contain maltodextrin. 

A lot of home brewing places sell maltodextrin and you can also get it from websites that cater to racing dogs (e.g. for the iditerod) as a dog supplement, but it's totally safe for human consumption.