A bit of history, I have the S4 for verizon, I run Vanir Rom and use Ktoons kernel. I also have a pebble watch that pulls weather every 20 to 60 minutes.
Prior to using in my phone, I used my external battery charger to ensure it was at 100% when I put it into my phone. Normally I charge every night but last night I said to myself, I want to see how long it will go compared to the stock battery.
Attached is a screenshot and I am well over 5 hours my norm and still have 27% left.
Personally, if you are looking for a good, solid replacement, I would certainly purchase one of these.
Link to the battery: http://goo.gl/UOg5DD