Flow batteries specifically are liquid, or more accurately fluid, there can be gas flow batteries, where the chemical sub-products are pumped in and out of the cells.

They tend to be large utility scale things that look like a chemical plant, correction, are a chemical plant with electrical storage as the product.

Liquid electrolyte batteries have been a thing from when batteries have been invented. But not much work has been done to really scale it up.

You might find the home made batteries of this guy interesting as well https://www.youtube.com/watch?v=eq7fR9ISuCw

It's not a new idea, they already exist.

A huge redox-flow battery is currently under construction in Switzerland https://www.swissinfo.ch/eng/climate-solutions/switzerland-b...

Ferrocyanide is not dangerous. Sodium ferrocyanide is used as an anti-caking agent in table salt. It's considered safe for this use in both the US and the EU, e.g.:

https://ec.europa.eu/food/food-feed-portal/screen/food-addit...

*ferrocyanide Less toxic than cyanide.

Potassium ferrocyanide: 1.6g/kg LD50 Potassium cyanide: 5mg/kg

So cyanide is approx 320 times more toxic.

Somewhat true, but consumers are buying vast quantities of lithium batteries and carrying them in their pockets. Those things are eager to catch fire and emit hydrofluoric acid.

You can have safe battery chemistry or useful battery chemistry. (Not an expert, open to correction.)

Yeah, just like no one would ever buy a lead-acid battery.

I don't think many people are concerned about their batteries being safe for ingestion.

The public is not going to buy a flow battery anyway.

Or perhaps they will, but only when public is taken in the context as in public utility or public city. But individuals are not going to buy a flow battery, it is a chemical plant.

Have to abbreviate it as FCN. Cyanide is ~320 times more toxic than ferrocyanide.

There are plenty of battery customers besides the usual suspects