Re: Do you guys think the battery will actually last all day with this device?
If you want all day battery life despite all-day use you need 3 things. A big big battery, a smaller, lower resolution screen, and a lot of optimization to make it all play nicely.
S5 has a large screen and not a whole lot more battery then the S4. Until hands-on reviews start trickling out, I'd say expect battery life similar to S4. The bonus is that the battery will probably be removable (I think - brain fart at the moment) which means you can buy a larger battery for it.
Or you can go with something like the MotoX which has great battery life due to optimization of it's processor, and a lower-res screen.