canon 1200d and 18650 battery

It is a battery case for the handle of the camera Canon Eos 1200d for sale on Amazon.

https://www.amazon.es/gp/product/B01F8VG5OA/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

my intention is to adapt 2 18650 batteries to give more autonomy to the camera ...