The S4 came out in Apr 2013... that's what I meant by an older phone. Did you buy this brand new in July? If I'm not mistaken, Samsung warrants the battery for a year after purchase. They will also replace it for free, but you need to ship to them, or find a local authorized dealer that can do it under warranty. Anytime a battery acts weird, it's normally the battery. Not much else can be attributed to it, and if it begins to charge faster, it normally means it's getting "topped out" more quickly... again, meaning a bad battery.
Contact Samsung, your carrier, or whoever you bought the phone from to see if the battery is covered under warranty.
01-29-2016 10:50 PM