Recently my phone has started having problems. When I charge my phone via the mains (AC) and use the phone to browse the web (or any task), it still loses charge. It gains charge when the phone is idle and charging, but much more slowly that expected.

I understand that intensive use of the phone can result in discharging even when connected to the mains, however I am not performing any intensive tasks / multiple tasks. I am doing the same things that I did before. Why has it suddenly happened?

Let me know if anyone can help me and what additional information I should provide.

Samsung S3 - OS 4.1.1 (Vodafone UK)