“Not much. All modern solar batteries that I’m aware of (mine included) have built-in fire extinguishing systems.”
Interesting, first I’ve heard of that - might you have a link to one of these “fire extinguishing systems”.
Mine are built-in to the batteries. There is a UL standard for it (UL 9540A). It stops the thermal runaway that causes the battery to continually burn. And, when a certain temperature is detected by the built-in battery management system (BMS) the battery shuts down. Without the thermal runaway between cells, they don't burn. And, the battery itself is designed not to burn in the first place. In addition to this, they may also have a built-in aerosol fire extinguishing system.