Are you using a 3Gs? It's well known that leaving it on will reduce the battery life by 10% an hour. If you're on 4.3.1, even connecting it to Wifi will reduce the battery life (this does not happen on 4.3.2 or 4.2.1)

My advice is for you to update to the latest iOS, and if you're not using 3G, switch it off.

You have 3G on all the time? This will drain the battery really fast and also heats up the iphone (which will further drain the battery)

Switch off the 3G if you're not using it. Also update to the latest firmware 4.3.3 as it specifically mentions that there is an improvement in battery life with this firmware.

I ahven't tried with the iPhone 4 but with the 3Gs on iOS 3.xx if 3G was on all the time, the iPhone will last a maximum of 10-12 hours. The phone will get really hot if you use 3G to surf the net for a long time as well.

I am on 4.3.3 for my 16GB iPhone 4, Jailbroken with tons of Cydia Apps and SBSettings will be the first Cydia apps I installed (Can't have my iPhone without SBSettings)

I have Wifi on ALL the time. I switch on Edge and 3G only when I need it (that's why I have SBSettings so that I can switch them off/on easily)

BT is OFF only when I am using Celeste which is rare.

Notifications is ON but not for FB etc .... I don't even know what's the use of these stuffs anyway

Location services is ON

I usually get 2 FULL days of battery and if I don't use it that much to surf the net, I get 2.5 days before the battery dies on me.

If I switch on 3G/EDGE, the battery depletes 2% every hour (without doing anything)

Good to hear that. When I read your post, I knew already that it cannot be 4.3.3. It has to be the battery.

When I had my Nokia N8, the apss that killed the battery was Whatsapp. I had to uninstall the app as it was connecting to 3G and trying to download data ALL the time.

Maybe it's the culprit as well for the iPhone 4?