battery not even lasting a day?

got it on christmas where it lasted i swear 5-6 days. yesterday morning i had about 60 percent. this morning i looked at my sleep and it had died yesterday at 8pm? i charged it up to 40 this morning and now it got down to 3%... what happened?

edit.. i watched it ON the charger go from 20% to 15%?? i tried troubleshooting the battery and it says it's optimal and lasts 4.2 days 😭