[Galaxy S III General] disclaimernotice:
Now, I know that we have a "All your JB discussions here" thread, but I think that this one is a rather specific issue and hence should be discussed in a separate thread. I also know this post is rather lengthy, but please read and give your opinions as it's important.

If you look at the last 5 pages on the JB discussion thread, you'll notice that lots of people are complaining about the battery drain due to wifi. The gist of it is that if you forget to turn off wifi before turning your screen off, then you'll experience a battery drain of about 5% an hour even though you're not doing anything with the phone.

I can vouch for the wifi battery drain issue. After flashing DLJ4, doing a factory reset, doing several full charge cycles, etc. here's what I can say:

On ICS, battery drain when the screen is off is the same regardless of whether you leave wifi on or off. Approximately 2-5% overnight

On JB, battery drain when the screen is off and wifi is off is the same as ICS. But if you leave wifi on, it drains about 2-3% an hour.

General battery use on JB otherwise is the same as ICS

It's pretty obvious. You don't even need to use apps to monitor battery use. Anyone can easily tell that there is something about the wifi causing battery drain.

So there are 2 things to note:

1) Wifi strength on JB is much stronger. For example, I could never connect to wifi from the 2nd floor on ICS (the modem is on the ground floor; it always shows poor signal and gives the "authentication error" when I try to connect), but now on JB I can easily do so within seconds of turning the wifi on. And this result is consistent each time I try.

2) With wifi on and the screen on at the same time (eg: when browsing), the battery drain is similar to ICS, ie approximately 1% every 4 minutes.

Point (1) seems to imply that the wifi strength on JB is stronger, and maybe the frequency used is higher. This seems like a pretty good explanation for the battery drain, until you consider point (2). Point (2) seems to indicate that the problem is not in the wifi frequency, as battery drain during screen-on time is similar (you would expect it to be higher), but there is some other explanation.

So my idea is that the wifi is indeed stronger in JB but that doesn't affect battery drain significantly. Instead, the problem lies in the fact that wifi management on JB is just bad. On ICS, when the screen is off, the wifi signals are probably "weakened" significantly, for lack of a more technical term, but on JB it remains at the same "strength" as when the screen is on. This is probably what causes the battery drain.

I'd like to use this thread to see what everyone else thinks from the experience on stock JB roms. And of course, if we can properly identify the cause, surely someone would be able to fix it.

Update 1: Alright, so far it seems that only those on stock kernels have this problem. Those on Siyah kernel appear to be unaffected. I'll test it out soon, and see if it can be a temporary fix for now.

Update 2: So I've been using Siyah kernel 1.7 RC1 for nearly two days now. While the battery drain due to wifi is reduced, it's still not as good as it was on stock ICS. And this is even after I flashed the "better profile.zip". Also, as a side note, the overall battery consumption on Siyah isn't significantly better than the stock kernel. But at least wifi battery draining seems to be less. Do continue posting your experiences so we can find a more viable solution.

Update 3: Over the last few weeks I've tried out DLJ1, DLJ5 and the leaked Rom with multiwindow (can't remember the Rom name). Anyway, from my experience, and from the collective opinions on people who posted here or in other battery threads, it would seem that the WiFi battery drain persists in all these jb roms. The only solution I've had so far was to use Siyah kernel. Some people report that custom roms work too, but I suppose if you're reading this thread it means you're trying to fix a problem with stock jb.