***[link|https://www.ifixit.com/User/4246912/etcabdi2011|etcabdi2011|new_window=true]*** if this is still the original battery, it is time to replace it. You can use [https://www.youtube.com/watch?v=H97kerb0Qjk|this video] as your guide. If you prefer a written one, use the written one [https://www.sosav.com/guides/mobiles/samsung/galaxy-day-4-plus/drums/|on here]. The steps are identical even so it is a slightly different model. The battery is available at many places, so pick the one you like.
If you already replaced the battery, make sure that you set your software to the most power saving features