[aurizon]

There are a number of flow batteries, where they have large vats where charge is stored in 2 discrete charge state fluids in a redox reaction. They charge a vat through a cell and discharge it in the other direction. Limits are solubility of the charge states in the transport fluid = huge vats for total watt-hours and huge redox cells for rate of charge/discharge. Runs well and vats are cheap. https://en.wikipedia.org/wiki/Flow_battery