iPhone 7 keeps losing signal.

See this Apple article: If you see No Service or Searching on your iPhone or iPad

If you see No Service or Searching on your iPhone or iPad - Apple Support

If you still don't have a 'service' after that, see -> iPhone 7 Repair Program for "No Service" Issues

iPhone 7 Repair Program for "No Service" Issues - Apple Support

Terry ~ 81% is not healthy and is to be expected in probably its original battery. Have the battery replaced and then see how the signal is:

iPhone Battery & Power Repair

About genuine iPhone batteries

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

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Terry ~ Does your iPhone 7 still have its original 5½ year-old battery?

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

Settings > Battery > Battery Health

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