Reportedly, Samsung has settled on the batteries with which it will equip the Galaxy Z Flip4. The changes from last year's model should deliver a higher battery capacity than the 3,300 mAh that the Galaxy Z Flip3 offers, but only just.
https://www.notebookcheck.net/Samsung-Galaxy-Z-Flip4-Leaked-battery-details-point-to-a-higher-battery-capacity-than-the-Galaxy-Z-Flip3.616555.0.html