While earlier reports suggested that the battery in the Galaxy S6 is not removable due to its design, newest report suggest that it is actually removable but it is far from being an easy task.
According to some of
the XDA Developer forum members, the battery is not only removable but the entire process is actually detailed in Samsung's instruction manual. While not being as easy as removing the plastic back, like it was the case on earlier Galaxy models and actually voids the warranty, it is still possible.
While that same instruction manual notes that battery removal should only be done by "your service provider or an authorized repair agent," and that its removal voids the warranty, you can still do it in case you want to risk it and take steps like "remove the circuit board."
The instruction manual part has all the shiny pictures for each of the steps and while it looks like something that should not be done by an average consumer, Samsung can still say that the battery is removable on the Galaxy S6.
Source:
Slashgear.com.