Update: Thanks for the advise, the reset worked a treat!

Took out and backed up the memory card, and reset the phone itself.

After installing most of the apps back, the battery now lasts a day and half. Before I'd charge at 9am at work, and it'd be 25% by 7pm with light-moderate use. If I didn't charge it at night, it'd be dead by morning, even on power saver.

Yesterday I charged at 9am, by 7pm it was 50+%. Went to bed with 48% and woke up with 41% without using power saving mode. Belting!