This very average frequency/amplitude/speed of discharge, for any given battery, depends upon many parameters (during most of such 'call to batteries': slope of the call and quantity of electricity needed, duration, proportion of vehicles connected to the grid...).

This is part of the solution, as we have ways to reduce effects of intermittency on production (mainly a mix spread over the continent), other ways to store electricity (hydro, green hydrogen-burning turbo-alternators...), and curtailment...