Samsung is set to unveil the Galaxy S10 phones next month. The biggest of the three, the S10+ will apparently be only 7.8mm thick, which would make it the slimmest phone ever with a 4000 mAh battery. In comparison, the S9+ with a 3500 mAh battery was 8.5mm thick.
https://www.notebookcheck.net/The-Samsung-Galaxy-S10-will-be-slimmer-than-the-S9-while-also-featuring-a-bigger-battery.394091.0.html