I love my new CF VV battery. It has the features I have said they should have put into VV batteries from the beginning. Anyways, when I got my battery the vape was great on my Nautilus tank. I run the battery at 4.8V and everything has been good until the other day. I had noticed a sharp voltage drop when the battery was close to needing charged. After charging it and doing very light vaping with the battery, after a day I was getting big voltage drops. I took it into the local shop. They have a 510 battery tester and the battery was hooked up without a tank at 4.8V it read 4.8V along with all the other correct voltages. When I put my Nautilus tank on the tester the battery would read out at 4.2V to 4.3V. I tried other voltages on the battery and the sweet spot was 4.3V.
As a test of the resistance the tank itself might be giving I hooked up a Smoktech Winder and Vision Spinner and both read 4.8V when set to 4.8V. I charged the battery fully and still seems like I am getting a voltage drop(cannot confirm due to not owner a tester).
Also, not that this is a big problem but I have noticed that the spring loaded connector tends to restrict airflow with certain tanks. Tanks like the T-Dux from Smoktech that draw air from the ego connector and draw it up from the bottom of the coils tend to loose airflow. If I unscrew it slightly, it fixes the airflow problem which makes me believe it is the connector giving too much pressure on these style of tanks and restricting airflow. I know that you do not support that tank since it is from another company but still thought you might want to know since people will be using other tanks from other companies with your batteries.