Under Settings then Cellular I have a message that states Error. What does mean ?

Tcrhe ~ This may be relevant:

iPhone 7 Repair Program for "No Service" Issues

Does your iPhone 7 still have its original battery?

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

Settings > Battery > Battery Health

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Please contact your Carrier.

It would be better if you can please re-post with a screenshot, in order to understand the phenomenon better. Images/pictures speak louder than words. 

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