Earlier reports claimed the Galaxy Z Flip4 would only get a modest 100 mAh battery capacity increase that would see it come equipped with a 3400 mAh unit. Word on the grapevine indicates otherwise, however, and for the better.
https://www.notebookcheck.net/Samsung-Galaxy-Z-Flip4-to-land-with-a-bigger-battery-than-previously-rumored.618275.0.html