OP asked about energy drinks. As you are asking about them, I am assuming that you are expecting to use the drink as a preferred source of fuel during exercise.
You should begin within 30 mins of exercise (drinking energy drink or an alternative or eat). You should aim to take in 30-60g of carb per hour. More your body cannot convert to glycogen (fuel)
isotonic sport drink (500ml)= 30g carb
Diluted fruit juice (500ml)= 30g carb
1 handful raisins or sultanas = 30g carb
1-2 bananas = 30g carb
To make your own isotonic sport drink:
200ml fruit squash + 80 ml water 1-1.5 g salt
or
500ml fruit juice +500ml water + 1-1.5 g salt (i use this one)
The salt actually encourages you to drink as well as providing some electrolyte assistance. Water on its own tends to quench thirst before you are properly hydrated.
Bingo… my advice is you don’t need to buy a sports drink. Make you own and eat bananas. I keep mine in my ass, so when im ready to eat its nice and warm 😯