An image of what is said to be the phone's retail packaging appeared appeared online, which showed details like storage and memory, but it didn't have any indication of the battery.
Now we have a document claimed to be a filing with the official Brazilian telecommunications regulator, Anatel, that reveals the battery in the Samsung Galaxy S9 will be nigh-on identical to the one in its predecessor, the Galaxy S8. It has a capacity, it says, of 3,000mAh.
If the expected Samsung Galaxy S9+ follows suit, that means it will have the same as the current + model too: 3,500mAh.
A previous rumour had pointed to the Galaxy S9 having a 3,200mAh battery, but this latest leak is more convincing.
Another, separate report, also suggests that the new Galaxy phones could be made of "Metal 2", a strong, light magnesium alloy as used in the Notebook 9 laptop unveiled at CES 2018.
A trademark filing for the name hints at Samsung using the material for future smartphones and wearables too. It might have come too late to be adopted for the Galaxy S9 and S9+, however.
Both new phones will be officially unveiled at Mobile World Congress at the end of February.