You gotta look at the bigger picture here...realistically.
If you're spending $1 or less per day on batteries, you've gotten your money's worth, and are spending less on vaping than you did on cigarettes.
So, on the expensive side, a battery is what... $25 ?
That means if that battery lasts you 25 days, you got your money's worth.
And if I spend $25 on a battery, it damn well better last at least a month...
And on the cheap side, you can get batteries as low as $8.
So get at least 8 days out of it.
don't worry so much about it, spend more time and energy enjoying the Vaping experience.
But to answer the question from my experience...
4 months, not a single battery has died yet. (knock on wood, now, hurry...lol)
And I don't even keep track, sometimes I vape till the battery dies, sometimes not.
I have on occasion charged overnight, but usually not.
So just use the batteries, keep a little stock of them, at least 3 or 4 available at all times.
And don't worry about them. If one dies, order a couple more.
Just clean the threads every now and then..maybe once a week or so.
I use rubbing alchohol and Q-tips.
Good to go.
My 2 cents.