Roger says his Samsung Galaxy S3 is having battery life issues. Leo says that every battery has a limited battery life of about 500 charging cycles, so he should just replace the battery and he should be good to go. If that's not working, then the charging system may be messed up, and a simple system reset should make the phone like it was when it came from the factory. Google will have already backed all of his data backed up.
He can go to Settings > Backup and Reset. It'll backup his account and data and then automatically restore it once reset. Then he can do the factory data reset and update his phone. He'll have to offload his pictures, though. The good news is that the phone is so old that he could probably get a free upgrade from his carrier.