Just a side note...
All of the li-ion batteries used for vaping are rated down to 2.5V for every discharge. They do not get damaged if discharged down to 3V or 2.8V or any voltage above 2.5V.
You might possibly, maybe, perhaps could extend the overall battery life a bit by not discharging below 3V (or higher). This is easy if using a regulated device as they won’t let you discharge the batteries below about 3.1V-3.2V or so (for most regulated devices).