I have a confession. I am a little bit of a battery nerd. Let’s face it, they are awesome. POWER! Okay lets get to the point. I found a great way to make an inexpensive Battery Bank that I have not plugged in. The key to cutting costs is scrapping. You can read this tutorial on Hackster I made The case itself is rather useful. Its inexpensive and a great way to control the quality of the battery bank. It is so great, I have built three. You can get them here: https://amzn.to/2TpKfD8 (yes that is an affiliate link. Using it is a great way to say thanks).
There are a few corrections I would like to make.
You need a solar powered lawn light
In order for this to be within $15, you need to find a Solar Powered Lawn light that you can scrap. This may be harder for some of you. If you cannot find one to scrap, you can find them on Ebay for cheap. Make sure that it is 5V. This might push you over the promised $15, however with this next correction, you might just make it.
USB C Adapter
I tell you in the tutorial to purchase a female to male USB to USB C adapter. USB C is still somewhat new, and as I was scrapping as much as I could for this projects, I did not have any USB C to salvage. However if you do have a USB C adapter, you could solder it onto the 5V solar panel and save yourself the $7.
Hope this helps you. If you have any problems or question ask below in the comments. In the future I am planning on writing a tutorial on how to scrap a battery for parts.