I've been off the charger for about 5 hours now and I'm at 4087 with about a 15 minute phone call and very little additional use.
No special rules.... I've just watched and learned that a good charge means when you take it off the charger, it will be just under 4200.... "like 4196mv or so"
I reboot to start the system timer over as its easier to clock how long I've been up and running since a charge that way.
I've also noticed when it gets below 3700mv, you have maybe 2 - 3 hours left depending on intensity of use.
I've noticed when it gets in that area, that allowing the phone to rest a while without using bumps the mv reading back up a to 3750 or so.
The lower it gets, the less robust it is at holding voltage under load.
When it gets below 3500mv it will start getting unstable and you will literally see the mv reading bounce around as you watch it.....and usually around 3350mv or so it will die.
All this is a little variable based on whether you have a load on the battery or whether your letting it standby.
Right now mine is charging and has been showing fully charged for about the last 3 hours.
While on the charger as I'm typing it says 4218mv
but when I take it off, it drops to 4160.
So I know I'm not truly fully charged yet.
After its been on the charger all night or for several hours..... 6 -8 hours or so, it will be just under 4200mv when "off" the charger.
I don't know everyone's habits, but I've noticed some people never put their phone on the charger till its in danger of being dead, then they put it on just long enough to get it back to full "or they think its full".... so basically it never gets fully charged.
They sleep all night with it off the charger.... maybe cause they are always getting text, or who knows?.. but thats the most convenient time to charge IMO.
If you do this and your unwilling to change your habits, I recommend you allow battery left to calibrate with your current use. But just don't be bewildered when you aren't getting the runtime other folks get!.. its not the batteries fault if its not fully charged!
It does not hurt the battery to not fully charge it, although you should try to do it fully at least every so often just to equalize the cells.
The updated battery left app has a calibrate button so you can recalibrate if you want to start the calibration sequence all over again to learn your new habits.
Seems my "total battery usage" changes if my total runtime changes.
So to some degree it appears to be learning even though it says 'accurate" on the readout.