I did battery calibration on my 4 month old S2 this morning. At 3.40am the battery is 100%. At 3.59am the battery drop to 97% only which minimal usage ( I felt proud since previously my minimal usage open browser and check message 3min will drop 1% ). Then i went to sleep and sadly when i wake up at 10.10am, the battery dropped to 79%! I didn't play anything but just open the wifi( previously before battery calibration, i always on my wifi and didn't drain the battery much like this). Is this some firmware problem or the battery need to change?