I am looking for a dual 21700 mod. The available ones, I probably will buy but, there aren't many to choose from. There are several single 21700 mods. My question is how long (on average) will a single battery mod charge last (I know this question is subjective). I vape around 65 watts, most of the ones I have seen online are rated 100 watts. I do not want to leave home and my mod die out because it was a single battery mod. I know I could carry a spare charged battery around, I just do not want to have to. Thanks