I thought it would be a great idea to build a lion battery pack with 16.8v that would last during an outage. 

It was fun, and I learned a lot. Of course I started with a few more 18650 cells than I should have. I thought, at first "well, they are batteries, right, more is better". 
And, I learned. I read, I consulted AI, though that was later, because AI wasn't very good when I started this project. 

Anyhooo.. since then, I realized that even though I have learned a lot, I needed to be very careful with these batteries, and I have cut the wires to my 4S ,4P controller board, and high quality 18650s. :-(

Lesson: It takes a serious look at fuse protection, and a high quality (do not believe claims from Aliexpress) battery controller. Build smarter than I did. 

Back to low voltage where I belong.

A high current battery power supply can start a serious fire by ANY accidental short or partial short that burns through to a ground or another wire.