Note: This post is about "Moderate" usage and battery life. I've done a similar test for battery life under "Heavy Usage" which you can find here: Heavy Usage Battery Life
-------------------------------------------------Well this is a rather pleasant surprise! I've had the Galaxy S II for a little over a week now so I feel it is far enough into its charge cycle to comment on the battery life...
This first picture is the phone's battery on around 60% charge on what for me is "moderate" usage after 15 hours. There are periods of inactivity, but over the course of the 15 hours I played a few quick games, browsed a lot over HSDPA, had constant gmail twitter + facebook push updates, watched a couple of YouTube videos and listened to a small amount of music. A couple of quick phone calls in there, too. I didn't have wifi turned on here because my HSDPA connection is around 4Mbps.
I think this probably represents fairly typical usage of a phone. Heavy usage such as transferring large amounts of data over wifi / uploading a video to YouTube obviously drains battery life a lot faster than normal.
This second picture shows the phone on the same charge as the first one, but you can see the battery drain is somewhat faster as I am watching more YouTube videos, making calls over skype and in general using a lot more data content (again no wifi). You can see this as the second, slightly steeper, downwards slope that goes in to the yellow.
The third "section" of the battery is the red section, near the end of the battery's life on this charge. I left the phone "awake" for a good chunk of that time, with several applications running idly in the background. This drains the battery somewhat faster than closing background applications but the drain on the battery is still looking pretty good. In case anyone is still asking if the Galaxy S II's battery can outlast a day, I thought I should include one final photograph, now with a "critically low" battery, having just outlasted the two day mark...!
[watch this space for updates]
I thought that battery life might be a chink in the armour of this mighty phone. I expected the the large display and the 2 x 1.2Ghz processors would eat the battery in a few hours but ... it turns out that the Galaxy S II can easily keep up with, if not outstrip, any competition in terms of battery life, whilst providing one of the smoothest and fastest user experiences I have ever encountered.
I look forward to the time when phone batteries will outlast a week. Battery-life has taken a huge hit since the start of the smartphone, but I do see the Galaxy S 2 as a step in the right direction. Samsung have not filled up a box full of magic and squashed it down into such a small package at the expense of anything: I really thought that battery life would be compromised but it just continues to amaze me. Wow!