Purge Mods Viper 21700 Mech Mod Vape Kit is so elegant and solid that it is best for cloud chasers. The fully adjustable button on the bottom will compensate for the battery rattle. With an adaptor. the Purge Mods Viper is also compatible with a single 20700/18650 battery. The Viper tapers to 28mm at the top which ensures for a minimum voltage drop and maximum output.