Why does my iPhone lose charge so quickly, even on standby?

A few facts
-iPhone 4s
-almost new condition but I've had it for a year
-I always close the apps completely so I rarely have apps running in the background
-a lot of my apps are set to manual with location services off
-I usually run down the battery on purpose by the end of the night so there is no unnecessary charging (which I'm told can also kill the battery)

Lately it's been running down unusually fast, I wake up, unplug it so its at 100 percent, by the time I get to work probably 2 hours later, I've barely touched it except for the occasional text and one quick read through Facebook and it'll be at 62 percent. Then it's on standby all day, not touched or used, but when I get off work 8 hours later it's completely dead.

It used to be of arrive at work with 96 percent and leave with at least 75 percent. And I try to take good care of it so I'm just a little confused on what could be causing the issue. Any ideas? Thanks in advance:)

If you have the LED alert light that flashes that causes the battery to run low and also your brightness runs the battery down if you have it all the way up say goodbye to your battery! Hope this helped

Well you could try reconditioning the battery which involves charging it fully then draining it completely then charge to 100% 4 times this can improve the battery quality and also try turning of push mail Bluetooth turn on aeroplane mode to and you could consider lowering the brightness:)

You need a new battery.

Lithium Ion batteries - which phones now use are much different from the Ni-Cad or NiMH batteries of a few years ago. With the older batteries it was the standard rule that you fully discharged them before recharging in order to maximize battery life. With Lithium Ion, the exact opposite is true. You DONT want to fully discharge the battery as this puts the greatest stress on the battery.

http://ezinearticles.com/?Forever-Charging-Your-Mobile-Phone?---10-Ways-to-Improve-Your-Mobile-Phone-Battery-Capacity&id=2234389

http://www.techrepublic.com/blog/five-apps/five-tips-for-extending-lithium-ion-battery-life/289