I think the Sonnen batteries here are small batteries designed...

I think the Sonnen batteries here are small batteries designed for home use like the Tesla Powerwall.

I'm sure Sonnen batteries are made up of many individual cells plus control electronics just like Tesla batteries (domestic Powerwall or grid-scale like the SA "big battery") and EMC's battery (which for example has used Samsung cells in some of its iterations). Sonnen may get their cells from one of the big suppliers such as Samsung, Panasonic r Sony.

From the article it seems that the Sonnen "Virtual Power Station" may work a bit like the Tesla one, where all of the batteries are internet connected, and allow Tesla to control them, for example to supply power to the grid in times of power shortage or high power prices. In the case of the Sonnen system, however, it seems that members of the community can sell to each other rather than to the grid. Exactly how this works I have no idea.

The Australian company Reposit has a similar capability which is in theory battery-agnostic, but in practice only works with a small number of grid-tie inverters (to which the batteries are connected).

In the case of the Tesla Powerwall 2, I believe the grid-tie inverter is built into the battery, so it's easy for Tesla to orchestrate their operation. I assume Sonnen is similar - the control smarts are built into the unit along with the battery and inverter. Note the inverter here is the one that converts DC battery power to 240V AC rather than the solar inverter that converts DC power from solar panels into 240V AC.