There are many mods at 3.7 volts out which use the 18650 batteries and I have read those go a long time, a day to several days depending on how much you vape. VP2, Protoge, several others come to mind.
the vp2 and protege use 14500 batteries not 18650.
18650 = 2000mah - 3000mah
14500 = 450mah - 950mah
Those numbers might be a slight bit off, but in the ball park.
18650 out last the 14500 batteries by quite a bit.
Prodigy and SB uses the 18650 batteries. Plus other mods.
what device can i use with the least amount of charging and the longest use time between charges?
Anything that will last you a full day regardless of how long that day might be for you should do the trick. You can go with smaller mods like the protege and carry an extra battery or two or you can go for a larger mod like the prodigy or silver bullet ( whatever fits your preference )
and only carry the mod. For me I like to use a smaller mod at times and a bigger mod at other times when I go out. Depending on my mood. Like if I go out to a bar, I don't like to carry my SB. I would opt for a smaller mod like a protege or Vp1 and maybe an extra battery in the pocket.
To answer your question, for a portable mod, anything that uses an 18650 battery will last you the longest. My silver bullet with a fresh 3000mah 18650 battery lasts me 2 days with heavy vaping. I'm just guessing you want decent portability even though it wasn't stated.
*A brand new stock 510 battery fully charged lasts me 1hr and few minutes. Just to give you some idea on my style of vaping.