Samsung s3 mini battery faulty
Ok I'm new to this so please bare with me. I have a Samsung S3 Mini which I've had for over a year now and all of a sudden my battery has decided to play up. I will have it on charge over night and by the morning it will say fully charged, then by lunch time it just switches off and it won't turn on until I've charged it. I work all day so rarely use my phone, might use it for the odd bit of browsing on my lunch but that's it.
I don't really have any apps on there either other than Facebook, Twitter and Instagram. So this morning I unplugged my phone which said it was fully charged, drove straight to the gym and when I went to check the time after like 1 hours of being in there it switched off and said I had no battery then when I got into work I charged it up and all of a sudden my wallpaper had changed to one of me and my partner which I don't have on my phone and it is an old one which someone else took which is on Facebook! I have no idea how that picture even ended up on my phone? Help please as it's driving me mad. Oh this has only just started happening over the past few weeks. Thanks everyone.