This weekend, in my adventures of being an Eco Warrior, I've been salvaging 18650 batteries from Ryobi Drill and Dyson Vacuum Batteries that were donated by people to me as the circuitry or PCB failed. I have collected 16 18650 batteries so far this weekend, and while they can be used in my Torches I'm wondering about a cool project I can work on.
Making a powerbank or larger 230v battery did not really appeal to me as I already have powerbanks.
The batteries are 3.7v and 1900-2000mah.
Portable CPU Fan: https://www.youtube.com/watch?v=R629INh0wlw
I've also been thinking of fun but dumb ideas like an electric esky(Haven't seen one before on youtube, only petrol).
Some other ideas I came across without full instructions:
Battery Powered Raspberry Pi Livestream Webcam
Super longterm: DIY Tesla