The growth rate is significant, but the structural shift embedded within it is arguably more consequential: the industry is standardising on four-hour battery systems rather than two-hour designs, and that transition reflects a fundamental change in what grid batteries are expected to do. A four-hour system can carry the discharge through the full demand peak and into the point where demand begins to relax. In Australia’s National Electricity Market, rooftop solar now regularly suppresses midday prices toward zero or below. In contrast, evening prices spike as solar generation ceases and industrial and residential demand runs concurrently. The second is indirect: the AI-driven surge in data centre electricity consumption is contributing to the evening peak demand growth that makes energy-shifting batteries more valuable to grid operators.