Hi NaOH! Welcome to Reovil! I know more experienced ReoNauts will chime in soon. For me, I've had to change out my batteries half way through the day and at the end of the day. I go through about 2-2 1/2 mil a day. So I would say if you have 2 min's going, you should make it through the day. Hope this helps out. And I love my Reo!
I'm a new REO owner(going on 3 weeks.) But have vaped quite a bit in the past(i really wish REO's were around when i started.) I've been fine taking my REO to work with me(filling the 3ml bottle beforehand, mind you.) And taking 1 fresh battery, and 1 spare charged battery. I work 8 or 9 hours usually, and depending on what i am doing i may be able to vape a little or a decent amount. But only once have i ran out of anything at work(towards the end of a shift i ran out of juice only because i forgot to top the bottle off before i went in; I now keep a little 5ml juice bottle in my glove compartment.) So far i can generally use 3ml of juice on 2 batteries. The second battery may die with a bit of juice left, but it's not an issue for me(i can't generally go through 3mls of juice in a work shift anyway.)
At home is another demon all together. But i always keep fresh batteries, so no biggie. I've been problem free with my mini and 4 batteries under any circumstances. I seem to be vaping about 3-5ml a day. I'm getting lower after the "awesome low maintenance" factor has started to recede. My first week i vaped like like a ..... sweats in church. The unit is that fun and awesome. When i first started vaping a couple years back, before i reverted back to analogs, it was a constant hassle having to top off,flood,switch batteries, carry a load of vaping "tools",juice all over my hands/mouth. It was a pain.
With my REO i enjoy vaping more then smoking analogs. It's great!
Now i just gotta manage to not eat more....since everything tastes so much better.
Welcome to REOville.....i hope you love it as much as i do!
-Prim