How is that possible? What OS version are you on? And, can you post screenshots?
What's your PRL?
I'm running AOKP b34 currently, but have gotten this battery life (within maybe 5% except for a few bad kernels or builds) pretty much consistently since I got the phone, even when stock (though perhaps 10-15% less there when on 4.0.2 - 4.0.4 does make a big diff fwiw).
I'll dig up some screen shots I've taken in the past. Let me find some and I'll edit the post.
Mind you, of those 40 hours, 16 or so is idle time. So really it boils down to about 84% consumed in about 24 hours for me if I don't charge at night. I do charge nightly now though, just in case I hit a day where I need heavy usage.
*edit* to add screen shots. This was from back on 3/22. I don't recall which build of AOKP this was or which LeanKernel it was, sorry.

But like I said, I've gotten similar results within probably 5% from AOKP build to AOKP build and LeanKernel to LeanKernel, though some are slightly better or worse than others.
Another note about this particular screen shot. In this case, I only had about 49 screen on minutes (was super busy at work), which is why I was up to nearly 50 hours

If I'd had double that screen-on time, it probably would have needed a charge around 40-ish hours.