Here's the recommendation from the manual:
We recommend you use IMR high drain 18650, IMR high drain
18500 or IMR high drain 18350 batteries, such as AW IMR18650,
IMR18500 and 18350 batteries. Other improper batteries may
damage iTaste SVD.
You can even run two 18350s for higher voltage availability:
There are two telescopic tubes available for the iTaste SVD; short tube
supports 18350 batteries and long tube supports IMR 18350(2), 18500
and 18650 batteries. You also can use 2 IMR high drain 18350 batteries
at the same time, which will give you the full arrange of voltages/
Wattages and proper power needed to use the device.
When installed with a single battery:
1. Red LED light = voltage lower than 3.6V
2. Yellow LED light = voltage 3.6V-3.8V
3. Green LED light = voltage 3.8V-4.6V
4. Red LED will keep blinking for 8 seconds when battery capacity is
lower than 3.3V, the digit LCD screen will show "LOV", Nixie tube
and LED cut off and then no vapor will be produced.
5. Red LED light will stay for 5 seconds when load short circuit detects,
then no vapor will be produced and the digit screen show “err”.
When installed with two batteries:
1. Red LED light = voltage lower than 7.2V
2. Yellow LED light = voltage 7.2V-7.6V
3. Green LED light = voltage above 7.6V
4. Red LED will keep blinking for 8 seconds when battery capacity is
4.6V-6.5V, the digit LCD screen will show "LOV", Nixie tube and LED
cut off and then no vapor will be produced.