If its still working the original way (earlier DNA40's) the battery meter estimates the amount of battery left by calculating off the last wattage the mod was fired at (goofy way of doing it).
Being that you're dealing with a temp controlled mod, the wattage can vary from puff to puff, so if you fire it without actually taking a draw (no airflow) it may drop the wattage way down then calculate off that wattage, ie show a much more full battery, then when you take an actual puff (with airflow) the wattage throttles back up and the calculation now shows a less full battery.
As far as i can tell, from my board, they have changed this with the DNA200 and the battery meter functions as it should, you can also change one of the fields in the display to read out the actual battery pack voltage.
Not defending their logic/methodology, but it never really bothered me on the couple DNA40's i have, though my vape habits/battery usage remain pretty consistent and easy to predict.