Arduino Micro/Nano battery Voltage and capacity meter.

Im going to build a pretty advanced portable speaker, thats going to be wired, and the source of the power is going to be 18650 batteries. For checking the voltage on them and the remaining power in %, ive chosen to build something with arduino, cause it can support displays and is pretty small. This is going to be the second ever project of mine where im going to use an arduino, if you are wondering, the first is a WS2812 LED ring Vu meter.

Main parts of the battery meter build, might not be the full list:
An arduino
18650 batteries
One of those i2c 0.96 inch LCDs

I have the plan in my head, but, as im new to arduino, and i couldnt find ANY projects for the thing i want to do, so, can anyone help me atleast with the hardware build ? Coding i could do with help from my electronics teacher. I have found a project thats somehow related to this, but it wasnt a 'status displayer' but a capacity meter: http://www.instructables.com/id/DIY-Arduino-Battery-Capacity-Tester-V10-/ , could also take some parts out of this code if possible and needed.