ask about iphone always restart

ckta ~ 81% is not healthy and is to be expected after years of use. Have the weak, aging battery replaced and the restarts will cease:

iPhone Battery & Power Repair

About genuine iPhone batteries

Repair Provider Verification

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

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cikta ~ Does your iPhone XS Max still have its original battery?

And, if possible before it restarts, what's the Maximum Capacity % here?...

Settings > Battery > Battery Health

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