Why is my iPhone battery so crap?

It bugs me so much I have literally just taken it off charge and its already 98% and I don't play on it all the time I don't even touch it sometimes and it gets so low it can't even last a full day

Did you over charge it? If you leave your phone on charge for ages it stops being able to hold it's charge and you pretty much have to have it on charge constantly. I did the same thing to my laptop.
Or… How bad is it? IPhones do an awful lot in the background if you have to charge it within 24 hours then no worries - they all do that.

Your charger could have a short in it which makes it take long to charge.charge it before you go to sleep and if it runs out slow your charger has a short in the cable take it back. Also remember that if your using like a iPod or iPhone charger it charges slower because its not the right charger.

If you have a warranty then I would suggest taking it back to the store and have it looked at. Because I use the iPhone 5 and have owned every iPhone and the battery is the one thing that always keeps me coming back to the iPhone.
I use my phone quite a lot and easily get through the day with battery life left at the end of the day when I plug in the charger.
But I do turn things off that I'm not gonna use, I always turn off Wi-Fi and 3g unless I'm actually using them. And I turn the notifications to manual so the phone don't keep checking for email etc.

Because it has high battery consumption. If you want it to last longer turn of the internet, wi-fi and don't go on games. If you do all that then the battery should last abit longer