Been using the Zeus 900mah for a few weeks and really like it. Was going to order another 900 in a couple weeks. I've been using it with large and small smileomizers and the dia difference of the large is really a small issue, but I was thinking if i'm gonna get another Zeus may as well get matching battery size for the smileo's. Really like the 900. if the 1300 works equally as well, but just last longer I guess it's worth the extra few $$$. Been using smileomizers for a while and use 3 per month (1 large and 2 small) so i'm fine with the longevity. Thx