The US installed a record 18.9 GWh of energy storage in the second quarter of 2026, yet installed power fell 7% from a year earlier. Duration, the energy divided by the power, got longer, and for utility-scale projects it reached 13,481 s (about 3.74 hours). If duration stretches to the 14,788 s average in the 2026–2031 outlook, a 10% rise in energy calls for only 0.3% more PCS capacity. Battery lines follow GWh and PCS-transformer lines follow GW, and each conversion unit carries a larger share as duration grows.