Built in battery kit
Fist of all a Built in battery kit is a kit where the battery is attached to to mod.
Therefore, you will find it included.
Because of the desire of having small vapes, these built-in battery mods are just perfect. Furthermore, you can charge the mod with a USB wire.
The USB wire is usually included inside the kit box.
Finally a built in battery can be as powerful as 4000mah.