Battery lower after power off (different each day)

I’d shut down my phone, and it’d be powered off for a few hours with do not disturb on & low power mode on to preserve battery life the best I can. Most days when I power it back on, it’s ≥75%. But sometimes it’s less than that. Today, it was at 58%. Anyone have an an idea on how to fix this?

(Max battery capacity is 88% if that matters)