Hekate's Denarius is a specialized coin that allows the storage and release of magical energies as electricity, heat, or whatever need needs fulfilling. Every coin has pips around the face of it indicating how full it is, and a categorization system for how much capacity each coin has. The system itself is designed to be used with specialized appliances, tools, devices, and more.
Coins come in three sizes in distinct categories of use, and then are further divided by actual capacity for each category. The grades of metal indicated below have nothing to do with the actual makeup of the coin, just the colouration of it.
The coins come in three different sizes and 9 different colourations, indicated above. The thickness for Sprite coins is 4mm, Chimera is 5mm, and Golem is 5mm. The pips are arrayed on each coin just inside of a ring bordering the edge of the coin, and can be seen on both sides. As a coin is used up, the faint glow on each pip fades one by one.
The Denarius relies on a simple interface. By reducing the magical components down to a single part, the coins are remarkably stable when produced and handled. The single part being, of course, the capacitor metal used to store the magical energies, formed from a specialized alloy. Coins can only be charged by using specialized apparatuses and never by hand.