I've got a Note 3 that, with "average" use, can go two full days without a charge, and in theory it has a worse battery than what they dropped into the S5. Now, if it's a slow day at work and I blow a bunch of time screwing about on the internet, it'll only go about 20 hours, so maybe what you're seeing isn't terribly inappropriate. Make sure you kill off your apps when you're done using them, and if you don't want to have push notifications, you can set your apps to check every 15, 30, etc minutes so that it's not connected to the internet and/or data 100% of the time. That will definitely offer up some increased battery for the long haul.

Having said that, I've yet to root a Samsung phone, but I've done it before with other devices. The biggest trick is making sure you clone your data just in case anything goes wrong. There's a great little app called Samsung Kies that will give you access to everything on the device - you can hook it up to your PC and do a full backup that way. Doing so over wifi is also useful.