The Samsung Galaxy S III has a removable 2100 mAh battery that lasts for 7.98 watt hours. This battery is only significantly outnumbered by Samsung’s Galaxy Note and is a step ahead of the 1800 mAh battery in the HTC One X.
I found battery life to be impressive and would easily last me through an entire day with sustained usage. It could stretch to two days of use with approximately 2 hours of screen time daily.
I tallied up my battery results from a few weeks of using the Galaxy S III and the results are as follows. It was on for an average of just over 19 hours between charges, during which the screen was used for 2h 45m on average and at the end of each charge roughly 35% was left over.
As a point of reference usage would include 30 mins of music playback, 50 mins of video, 15 mins of gaming with the rest of the screen time taken up largely by checking email, RSS feeds and browsing the internet. While at home it was connected to my Wi-Fi network and outside of that mobile data was enabled with auto-syncing of many accounts.
I believe that other users can produce even better statistics than this with only a few basic tweaks that anyone is able to set up. Comparatively, this is leaps and bounds ahead of what I experienced with the HTC One X.
Heat issues were basically non-existent during my entire time with the Galaxy S III. The only times I noticed it heating up was while playing graphics intensive games and the rear of the device warmed to touch. Unlike the HTC One X this heat did not spread to the display or start to concern me in anyway.