Why won't my phones battery die?!

I have a nokia pureview that came out in 2012 I think, and I've had it since 2013. The power and volume buttons don't work, and sometimes when I watch videos, the screen freezes, and becomes static looking. Since the buttons don't work, I can't soft or hard reset it, so the only way to reset it is to let the battery die. It's been 12 twelve hours and it still hasn't died. It never lasts that long. Even when it's working there have been times where I've had it in my pocket for hours without using it, and it'll die typically before even 8 hours of inactivity. I've even been setting it out in the sun hoping that the heat will cause the power to run out sooner, but it still is on. Any idea why it's lasting longer when it's not working than it does when it is working?It's still ridiculous that it's still on. I wish my battery usually lasted this long.

Also, do you know why the buttons no longer work? And is there a way to fix it without taking it in?

Thanks for the help!
Added (1). Also before you ask, the battery cannot be removed. I've looked it up and it explicitly says that it can't, and that's what the soft reset feature is supposed to replace.

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