The iPhone 4S definitely has a harder time lasting through a full day of use than my iPhone 3GS did. After a good 12 hours of standby and three hours of use, my 4S is usually down to about 20%, if not less.
This morning I found myself taking an hour-long subway ride with just 2% of my battery left (I may have forgotten to plug in overnight). I expected a dead device within ten minutes of stepping onto the train, but I decided to set the iPhone to Airplane Mode and turn brightness to minimum – just to see how long it could last. I started an album up, put my earphones on, and waited for the music to suddenly go dead. But, to my surprise, the 4S managed to last for over an hour with the screen and radios off, playing First Aid Kit’s “The Lion’s Roar” all the while. The 4S even managed to squeeze off two shots from within Camera+ before dropping to a blood-red 1% battery.
It’s no surprise that turning Airplande Mode on and turning the screen off saves battery life, but I was really surprised by how long the iPhone can function when all it’s focused on is pumping out tunes. Two percent ended up lasting over an hour, and yet I can regularly lose 10% or more on standby when I leave 3G on. But then there are times like today when battery life can really, really surprise you.