Hi, I found this forum by looking for solutions to the same problem. I have just bought Galaxy S2 (second hand) and the battery does not hold charge (in this case of a picture I did not touch phone for all day neither made/received any call as I even removed a SIM card)
I checked "Battery usage" and noticed that "Cell standby" sucking the most of the batteries energy- even 75%!
What is Cell standby for? I am not using any SIM card with the phone.