Battery Issues

My mom bought a phone at Markham but the phone had issues with the battery. She took the phone back to them, they took it said she should come back 6 weeks later. A 2-3 weeks later she got a call that she should come and fetch the phone. When she went she got a note that read screen and battery replaced, yet there was nothing wrong with the lcd in the first place. Long story short the battery still lasts for a day with her not even touching the phone.