Sudden drop in battery life I used to get average good battery life, i.e. for about 2 days without re-charging, since yesterday my Samsung S2 battery life has become terrible, I haven't installed any new applications.

What could be the reason for this?
Go to Settings - Battery and take a look at the usage. You should see if there are any apps using an unexpected percentage of battery life. I've also seen location based apps drain my battery, but that's not saying that's what's causing your issues though.