It already exists. It's called a flow battery. Basically it's a fuel cell that can run in reverse - recharge the used electrolyte/fuel allowing it to be used ag

It already exists. It's called a flow battery. Basically it's a fuel cell that can run in reverse - recharge the used electrolyte/fuel allowing it to be used again. There are many types. They are not used because they don't have the same energy density as Li batteries, plus other disadvantages. https://en.wikipedia.org/wiki/Flow_battery https://en.wikipedia.org/wiki/Flow_battery