iPhone takes longer than usual to recharge after dying

I’ve had this iPhone for the past two years and have been taking good care of it, no water damage, no hard drops, etc. In addition to being gentle with it, I run it down until it dies once or twice a month, as I’ve heard that this helps it “reset”. Usually I do not have a problem with it turning back on and charging normally, but this past month, it has been taking hours just to turn on after dying, even if it is plugged in seconds after the spinning buffer circle of death pops up on screen

I have switched cords, changed when I’m charging it, and even tried to reset it. No dice. It’s definitely charging, according to the screen, but it just takes hours to turn back on and when it does, it is at an absurdly low number, like 8%, despite the fact that it has been charging for literal hours.

How can I fix this?