I would like to know if there is an application for a 48v master/slave battery where there is a master and up to 9 slaves can be connected in series to make a 480v battery?
The master will be about 5k more expensive then the slaves but this allows for protection across all the cells in all the batteries. It would also have active balancing across the entire string.

I know at one point there was a SolarEdge setup -- I do not know if SolarEdge themselves did this or someone else -- that incorporated a high voltage Tesla battery. I don't know if you are familiar with the SolarEdge setup, but they essentially strap the boost stage to the bottom of the panel (so you get panel level MPPT for free) and they have one high voltage supply coming from the roof (around the 400V mark if I recall). The "ground unit" therefore needs no boot stage and like most "transformerless" PV-inverters, it makes AC directly from the high voltage DC.

By placing a high voltage battery in this system, they could store excess PV in the battery and use it at night. SolarEdge inverters are grid-tied and normally don't work at night.

Tesla batteries are not really readily available in SA and even though I hear noises about it every now and then (Rubikon is the importer?), it's also quite expensive.

In other words... there might be a market opportunity for a high voltage battery here. Sorry, I don't have more details.