The greenish/black residue is normal buildup on the threads and post of your batteries due to the presence of moisture in an environment where electricity is passed from one metal contact to another. It's a combination of very trace amounts of metallic corrosion, burnt sugars from efluid, and impurities naturally occurring in the air.
Rubbing alcohol can be used, but is not recommended because if it is not fully evaporated from the battery or carto when you resume using them, vaping the residual rubbing alcohol has serious health risks. If you do decide to employ rubbing alcohol, get the one with the highest concentration of alcohol content and let your batteries and cartos dry THOROUGHLY. I have several friends and family members who, though they do not consume alcohol, keep a small bottle of Everclear just for cleaning batteries and cartos.
as for what to use to get the most out of your vape, I would recommend a Dial-a-Volt in either manulal or automatic and a 3.5ml tank. Or, you could wait and see what the upcoming "next big announcement" will bring. I hear that it is an awesome unit!
I hope this helps!
thanks. thats what I wanted to know if I could use the alcohol cause I surely can't afford to keep buying them.