I guess my issue is I am a newbie when it comes to the 2.5 Provaris. I came to the party with a P3 as my first Provari and so I was a bit backward from everybody else in that I learned to use that menu system comfortably first. Now I just got my first 2.5 last week and have the learning curve of a "new" menu system, with its own unique style of battery meter display.
So I'm still figuring out what 3.6V means in terms of battery life because I'm used to seeing 53% left instead. And not having a screen light up every time you press the fire button seems a little strange to me right now because I've gotten so used to reading the P3 screen. It's a different experience entirely. I just need more exposure to it.
A full battery reads in a 4.2, but will move off that quite quickly (because technically that's being boosted from the base 3.7 voltage the battery puts out). Most 2.5's will begin blinking at 3.4, then cut off around 3.2. It'll hang at 3.7-3.8 for quite some time. Once it drops from 3.7 you're literally in real-time.
You'll quickly come to know approximate life of each battery type, and a clock will probably be your best indicator (once you gain some confidence and understanding).
My batteries rarely ever even make it to the blinking point. I swap 'em.