Unable to boot iPhone 7

That aging, original battery is inevitably very weak after years of use and cannot provide sufficient power to start up your iPhone 7. ...So have the battery replaced and all will be well:

iPhone Battery & Power Repair

About genuine iPhone batteries

Repair Provider Verification

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

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Changing the battery may or may not solve the issue. I have and iPhone 4 and 7 and both still have their original batteries and both still work perfectly fine. If you can't get it going have your phone examined at either an Apple Store or an Apple Authorized Service Provider. In the meantime some additional help:

If your iPhone won't turn on or is frozen - Apple Support

Force restart iPhone - Apple Support (CA)

Restart your iPhone - Apple Support

iPhone - Official Apple Support

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

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