Continually scanning for network drains battery, but I've got network?
Setting the "Preferred network type" (under Settings / Wireless &amp; Networks / Mobile Networks) to "3G" (instead of "4G (recommended)") causes the phone to report a valid network connection and seems to solve the battery issue.

In Android 9, this setting is under Settings / Network &amp; Internet / Mobile Network / Advanced.

Remember to change it back once you're home.