yep,I know about c tank, I have a ego T. the reason I was asking is the e-cab and the tornado ego c slim, is that they both use replaceable battries, a lot less money when a batt. croaks. I tried my first e-cig. and never had to have a analog again. thats after smoking 3 packs a day for 55 years.had to quit because I have COPD. I though it would be really hard, but it is easy.thank goodness.