Enerox, page-8

Yes that's true - in fact the current 10 kWh battery actually consists of two 5 kWh electrode stacks bolted together. I understand one of the manufacturing cost reductions in train is replacing this with a new single 10kWh battery stack.

I don't see any huge advantage in a larger (and therefore heavier) battery. I believe the ZBM2 is the smallest and lightest flow battery on the market, which is an advantage in terms of deployment logistics. The BMS allows multiple batteries to be managed as a single logical entity, so multile batteries doesn't add operational complexity.