Electric double-layer capacitors are a newish energy storage technology. I find them fascinating and I want to play with them.
Like a capacitor they can charge and discharge very quickly due to their low equivalent series resistance.
But supercapacitors store roughly two orders of magnitude more energy than normal capacitors!
I bought five 3000 farad, 2.7V Boostcaps:
I machined aluminum strips to form connecting bars. A 13.5 V series stack: