I hacked my note 3 to take external battery via xt60 plug. With a 1S16P battery pack, it now powers my phone easily for 2 and a half days of use.
Step 1: Hack the Battery Pack
peel back cover, detach cells or cell, wire positive and neg to circuit board. cut up a few used credit cards or casino cards or those plastic cards that came in the mail to fill the blank.
Step 2: Connect Your Interface
forgot pictures. Just solder in xt60 plug to connect battery pack.
Step 3: Decoration
I didn't do this with mine, but I should. I was on a road trip and went to pump gas. I swear a police officer approached me thinking it was some sort of explosive device... After I explained it was my battery he drove away, but he looked upset. Sorry for the way it looks. A simple black bag over it would help.