Difference Between Mod and an eGo or EVOD Battery
eGo and EVOD batteries are both battery types with the power cell built in (and non-removable). They generally feature a dual 510/eGo threaded connector built in for attaching atomizers.
'Mods' on the other hand are a shell that you put replaceable batteries into. Generally these will accept 18650 or 18500 type batteries.
It is important to note that most mods will REQUIRE a flat top battery (no little nub at the top). These 18650 and 18500 batteries will generally be 'unprotected batteries' with especially high discharge rates. These are not the same as your average AAA batteries and it is important you are familiar with proper handling of this type of battery to prevent injury and fires.