I recently purchased this Nathan Synergy bladder to go in my running vest. It has two chambers. One for water and one for electrolyte drink, holding a total of 80 oz. I tried it out for the first time yesterday. My regular bladder only holds 70 oz., but this one still fits in my Nathan Intensity pack. It's a little bit of a squeeze, but nothing out of the question. I really liked having the electrolyte drink. I didn't have to eat as much on the run, which was nice. The tubing is a bit long, but I think I might just trim it up a bit. Overall, I'm thrilled with it!
Toggle that switches from electrolyte drink to water.