Just picked up a used galaxy s4 last week. Battery life has been incredible in my mind.
Took off charger 36 hours ago. This includes about 30 minutes talk time. 10 text messages. 1.5 hours of pandora. 6 hours wireless tethering via FoxFi, where i streamed 6, 40 minute episodes, and about 2 hours internet browsing. Between the 18 hours of work, I had a lot of downtime to browse the internet, and use it probably a half hour between all the breaks. I'm at 24% now.
Overall I'm very happy with the battery life.
I'm rooted, running a permissions manager, and firewall, where all but essential apps are blocked. I also set all updates to manual. I think these three things have affected my phone's battery life significantly.