How much does price forecast accuracy affect BESS revenue? Electricity Maps and FlexUp ran an eight-month simulation in the German day-ahead market to find out. The Electricity Maps forecast outperformed a naive persistence baseline by €4,860 per MW and captured 90.7% of maximum achievable revenue. The study also shows why MAE, the metric most forecast evaluations are built around, is a poor predictor of revenue capture, and what to use instead.