The looming retirement of much of the nation's coal fleet combined with electrification-driven load growth is focusing attention on the need for firm resources. At the same time, the influx of intermittent renewables is increasing net load volatility and creating a need for fast-ramping flexible resources. Utilities across the country are wrestling with how to meet these needs by investing in portfolios that balance affordability, reliability, and climate. More often than not, the choice comes down to batteries or gas. What role will batteries and gas play in a decarbonizing power sector? Are they complements or competitors? What other resources can provide these services?