You obviously need to ask the question a different way. I have had a battery certificate from that very dealer for an ID.4 (not the one I bought).
I would guess the sales rep doesn't know what you mean by state of health - most of them know almost nothing about batteries and that email is a perfectly reasonable response to the literal meaning of the words.
I would go back to them and clarify that you'd like to see the battery certificate that is produced for approved used cars showing remaining battery capacity and related data.