This is something that we also hate about the iPhone. The iPhone 6 and Galaxy S6 don't come with removable batteries. What this means is that you're unable to install an extended battery for more juice and you're forced to take the phone in or send it away if you need a replacement.
In our time with the two devices, they've exhibited solid battery life though that's not the case for everyone. Many Galaxy S6 users hate the device's battery life. It was also a feature that critics complained about in their reviews.
We don't hate the battery life on our Galaxy S6 but we hate the fact that we have to buy an expensive bulky case to add extra charge.
Mileage is going to vary but this could certainly be a problem for those of you used to getting excellent battery life out of your current device.