iPhone 7 plus Messaging draining battery

I gave my Mom my iPhone 7 plus a few days ago wiped clean. She took it into Xfinity and they put a sim card in and restored from iCloud and the battery now drains excessively fast. She had it looked at and diagnostics show the battery is fine, but 80% is being used by Messaging. My Mom hardly uses her phone, but does text. Everyone seems at a loss. How does a phone go from being fine, switching carriers, and then all of the sudden the battery life goes bad? There must be something we are not seeing, as well as all the techs who look at it.

It is on the most up to date IOS version.