Found a great 5v battery supply for porjects that need regulated power, Also, need help from anyone who owns one.

18650 Battery Box, it holds 4 18650 batteries, and gives a regulated 5v power supply. I just ran an arduino mega, rasberry pi, and a wifi dongle off of it in a rocket for about 4 hours.

I also wanted to know, does anyone have one? And how do I know it's charging?