So I heard back from Evolv regarding my experience with only getting 16 hours from a fully charged battery.
Here is what they had to say:
To be honest we have been amazed at the customers who are reporting 24 to 36 hours between charges. Our original testing suggested 12 to 14 hours between charges or approx. 1 to 1.5 days of vaping between charges. Don't get us wrong we were thrilled to see such battery life but it was certainly unexpected.
The email went on to explain the life expectancy or the batteries, etc... And they did offer to swap out the batteries for me right now if I wanted them to. In all honesty, I am not displeased with my battery performance. And hearing from Evolv that they had not expected longer of the battery has put my mind at ease, so I don't think I will be seeing any performance issues in the future, but also know that Evolv will stand behind the product if I do. So I'm just going to keep using it, and keep happily vaping.
On another note- My wife, who I have reported before as saying that the Darwin was too "masculine" looking for her taste. Well, she is getting fed up with her finicky Turbo AV, getting fed up with replacing batteries repeatedly, and every time she takes a drag off my Darwin she says "that thing just hits so perfectly every time"... So last night she says "ya know, I think I'm over appearances and just want something that works perfectly every time". So yeah, I'm thinking a 2nd Darwin will need to be ordered soon.