Some real good advice here as usual, but I have a hunch that Aral seems to want to chart their own course, by sticking with auto 901 batts. I can understand, and we each have to learn what we like and what eventually works best for each of us.
That being said, I cannot resist saying that I was strictly an auto 901 battery user, with the 901 atty, for about a year and a half, refusing to try anything else, as I was really happy with the performance, the feel, the portability, and the vapor of the DSE901 system. So I bought ALOT of batteries and ALOT of atomizers. I always had at least two batteries charging, and when I hit the road, made sure that I had about 5 or so batteries along for the ride...
Then they changed the construction of the 901 atty to V2, with a metal disk enclosure that, to me, created a leaking, badly performing bugger of an atomizer. I just did not like it anymore and searched and searched for the old style in vain, that's how much I liked the 901.
Long story longer, I tried a great mod, with cool customization, and liked it alot, but strictly for home use as it was a pain to carry around (I like having my vape in my shirt pocket to whip out at will).
That's when I found the Riva 501, and I have not looked back. Damn, it really makes a difference going almost all day on one battery, with great vapor, taste, reliability, etc. It really fits the hand nicely and just isn't that much of a difference from the 901, compared to all the crazy, bulky mods out there. It's a classy vape. Granted, I have still stuck with 501 atty's and they can be hit or miss, so I do not blame anyone for going the carto route. I just like what I like, and have found my working system, so I stick with it for now (other than trying more reliable 501 atty's and perhaps those even longer lasting batteries). At least until I know better...
So, I guess I am saying, Aral, go your own route and see where it leads you, and the very best of luck. But if I was to suggest something else for you (even though you didn't ask, really), since you are going the carto route, I don't think you could do much better than "Riva 510 carto Deluxe" kit featured at LF for like $34. Throw in some juices and you are good to go. And good to go for a much longer time than with the standard 901 batteries.
Again, just my personal opinion. As long as you are on the vaping trail, more power to you!
Aloha,
Kona