iPhone charging slowly at night

I have an iphone 13 and it charges very slowly at night for no obvious reasons. I believe it has something to do with optimized battery charging but why does it only charge around 15 to 25 percent over night or from around 30 to 46 percent (1am- to 7am) running nothing but to 100 from 20 in only a 4 hours while playing YouTube during the day. If it is the optimized battery charging and it’s still learning my routine, why doesn’t it charge anywhere close to 80 percent?