Since it takes at minimum 4 hours to drain each battery (3.3KW discharge rate), a better question would be what percentage of peak demand power they can provide.

Max power: 3.3 * 50000 = 165MW. Peak demand for 2020: 47121MW (18th August 15:57). Percentage of power: 165 / 47121 = 0.35%

Using the yearly average instead (31713KW): 165 / 31713 = 0.52%