https://wccftech.com/galaxy-s9-plus-battery-same-as-galaxy-s8-plus/

The Galaxy S9 Plus is expected to be a better choice for consumers who looking to upgrade to a larger device this year. It will come with its own array of exclusive hardware additions, but the one thing that we are not looking forward to seeing is the battery capacity. According to a leaked image, the Galaxy S9 Plus will feature the same battery capacity as the Galaxy S8 Plus, which is a 3,500mAh battery.

While we do not expect these cells to explode in the same fashion as the cells present in the Note7, we were hoping for a higher battery capacity from this image. Fret not though, because there will still be an advantage of using the Galaxy S9 Plus when it comes to battery life and no, it does not involve the efficiency of the SoC.