Hi am just using iphone 13 since 8 months and also used task like gaming it dropped battery 
health to 90 % it is ok or not.
for gaming or high screen on time, its normal to see battery health reducing bit faster than regular users bro. when it reaches 80% and if you notice any fast battery drain and not able to use like the way you do normally before, then you can check with apple service center to replace the battery. then it will again perform better.
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Thank you bro for your reply…
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