my wi-fi is not work

adarsh ~ 80% is not healthy and is to be expected in such an old, original battery. So have the weak, aging battery replaced and your Wi-Fi will probably then function normally:

iPhone Battery & Power Repair

About genuine iPhone batteries

Repair Provider Verification

(Articles found by searching Apple's Knowledge Base.)

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adarsh ~ Does your iPhone 7 still have its original battery?

And what's the Maximum Capacity % here?...

Settings > Battery > Battery Health

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