https://wccftech.com/galaxy-s9-battery-capacity/

This year, the Galaxy S8 had lots of things going for it, except for a stingy-sized battery capacity and that awkwardly placed fingerprint sensor position. Next year, Samsung could be addressing these issues and the one thing that customers should be looking forward to is a bigger battery from the upcoming flagship.

Galaxy S9 rumored to feature a 3,200mAh battery as opposed to the Galaxy S8’s 3,000mAh is expected to be a minor change. A new rumor out of China states that the Galaxy S9 will have a bigger battery when compared to its predecessor so, by that comparison, we should also believe that the Galaxy S9+ will also have a bigger cell when compared against the Galaxy S8+.