Ummmmm. A Lot!! lol
I use both 18650's and 18350's in different mods simultaneously. I'm usually running between 4 - 6 mods at once with different juices, builds, ohms, dual and single coils, etc. And, I've got a DNA 30 arriving tomorrow. With so many variables, it's hard to compare "apples to apples". But I find that, except for sub-ohm vaping, a 18650 battery lasts me about a half a day of moderate vaping. I say moderate because I'm using more than one mod at a time. A 18350 lasts me a bit less than half a day based on the same type of use. I keep the charger on my desk and always have spare batteries charged and ready.
