As a reference I use my dual parallel box with a 0.3 coil all the time.
I get about 4-5 hours of my normal chain vape ( puff it like I did when I smoked, so maybe 5 minutes of chain Vaping ever half hour or so) and I use vtc5 batteries.
So I carry a spare set to change out at 3.8v ish
I use 0.3 because of the voltage drop at 0.2 seems to give the same vape as a 0.3 after everything else is worked out, but that's my box, yours may be better.