Why doesn't the iPhone 4s battery last?

This is annoying me so much. I swear I charged my battery to 70% took it out, by 1 hour of using it my battery just decreased to 35%! Why? I have to charge it every 2 hrs or just use it and keep in the charger.

Has anyone experienced the same? Is there a way to increase battery life?

And if this helps, my iPhone is actually jailbroken. But ever since I updated to 5.1.1 my battery has been a total nightmare.

I just bought one and yeah i noticed the battery life if pretty poor, as soon as it is used it drains the battery.
The only thing I found helped was removing apps that constanlty update through the internet. And turn off wireless so it isn't always searching

I have an iPod and had similar problems. You should:
- turn your brightness down to about 1/4 to 1/3 of full brightness. It will save loads of battery and you'll get use to it eventually.
- Turn off Wi-Fi when not in use. Quite annoying to keep going to settings but Wi-Fi drains battery about twice as fast as non-Wi-Fi
- disable notifications for apps you don't want them for, so it doesn't waste power constantly ready to retrieve data
- Disable location services for apps you don't need then for (I don't have them on at all)
- restore your iPhone, but tabs fee purchases and backup first.

Its proobably coz its such a big fone and takes up so much energy plus its full of apps and if your constantly on fb and listenin to music and texting, on any fone it runs he batt right down. You can change the settings so you can save energy by making the light lower and stuff etc.