DIY DSLR/Mirorless camera power base/grip

Hi. I'm looking for a way to build my own powerbase/grip for my lumix g85 camera by using a power adaptor, long charge battery cells and something that can allow the user to see the remaining charge (because on the g85, whenever you use the power adapter, the power/battery level isn't showing on the LCD screen since it's no longer in the cam). I'm inspired mostly by those two youtube videos:

https://www.youtube.com/watch?v=HL_U_tl3Q20&t=903s

https://www.youtube.com/watch?v=GYvf77SRUQ0

The reason why I would like battery cells instead of an attached small power bank or even Canon batteries is because I want to house everything safely in the base (no loose wire/cable anywhere on the cam and solidity in the base so nothing can break and fell  by accidend). Although, I don't know if it's going to require a power regulator and/or converter. My knowledge on electronic is very limited, which is the reason why I'm asking for some help & advices on how the proceed. 

Anybody who's interested & with the required knowledge here would like to help ? Please let me know.

Thank you