I have noticed that Whatsapp and IE are big battery consumers..and that is what I pretty much use.
I did a hard reset yesterday on my l920 and started as fresh, reinstalled all my apps since I was not getting more than 15 hours at full charge.
After the hard reset, at full charge I had 1 day and 15 hours left, my last charge was 15 hours and 35mins ago (during the night) and I still have 1 day and 2 hours left (74%) BUT with a LIGHT use of whatsapp and a few texts, thus the phone is fine handling the BUILT IN SMS plataform but not the others app.
After the hard reset I still notice the extreme loss of Battery from Whatsapp, around 30% per hour, sometimes even more!
I have just started using BBm, I have too see if the battery loss is the same as Whatsapp.
But at least, the hard reset did improve my battery life! 15 hours at full charge vs 40 hours...
Just in case, I have everything blocked except Whatsapp and BBm. Wifi ON, Data OFF. Email set to Manually.