The BOGO 400mah VV 510 Thread batteries pack a lot of features into a small package.
5 clicks to turn it off/on for safety.
3 clicks to switch output voltage (Green light = 3.4 volts, Blue light = 3.7 volts, Red light = 4.0 volts).
2 clicks to activate the preheat function
You will get (2) batteries AND the USB charger... What a great deal! You will need to remove the cartridge in order to charge the battery.