6.1.3 is fine for battery on my 4S, no problem at all. I don't believe there's anything wrong with it; that doesn't mean that other people aren't having problems, I just don't believe those problems are caused by 6.1.3 per se.
On pretty much every version of iOS, I've had the occasional bad day/few days battery life, times when I've noticed seemingly sudden drops and started obsession over the percentage.. this isn't just with the 4S either, but with my 3GS and 3G before that. To be honest I think I was happier back in the early days when iOS didn't give you a percentage reading for battery at all, just the gauge (you can still turn off the percentage now in the settings, try it, it might make you feel better).
The point is, these problems are universal to iOS and pretty much every other OS for that matter, there is no "good" version where everyone has great battery life, and no "bad" version that burns up everyone's battery in seconds either. Search for "battery life" and ANY iOS version number and you will find a ton of posts to say that version (whichever it is) has bad battery life and should be avoided, because somebody somewhere is always going to be having a hard time of it and blaming that new update.
If things are really bad, backup the phone and do a DFU restore, you'll be surprised at how much that can fix.
DON'T live in fear of new iOS versions, just accept the update and move on. The advice being peddled here to stick with what you know, if it ain't broke don't fix it etc, is nonsense - if it wasn't broken there wouldn't be an update. The purpose of these updates is to patch flaws, including battery-sucking problems and sometimes major security issues.
Much is made of 6.1.3 cutting off the jailbreak (boo hoo), less is said of the fact that the jailbreak exploited some gaping holes in iOS security in order to work. If Apple hadn't patched those holes, they would be completely negligent, and leaving the door wide open for others to barge through. The longer you sit there on comfy old 6.0.1 or whatever version you've decided to settle on forevermore, the greater the risk that someone else is going to exploit those same weaknesses to do something really nasty to your device and your data.