I was thinking about buying a zmax and was curious on what batteries work in these as far as 18650 go. Do they need to be button top or flat top? Will protected batteries work or are they too long? I am looking to get the highest MAH battery I can get for the longest battery life and was wondering what battery will work. For example panasonic makes a 3400 mah battery I was wondering if it would work in the ZMAX. So if you experts can recommend the highest quality, longest lasting battery that will fit in the sigelei ZMAX I would appreciate it. Thank you in advance, this forum is the foremost authority on the electronic cigarette industry and I appreciate all you guys do.