There can be several reasons for a low battery in the afternoon:
- the battery can be out of order and with some smartphone it's recommendable to change the battery
- when you try to have a stable battery until the evening It's useful to get in flightmode or turn off your smartphone, then the smartphone is not trying to connect to the internet or to search a mobile network and you can save some battery
- in same cases it's possible to control your apps which apps try to get connection to the internet and use a lot of battery so you can disable these apps