Glad to see I'm not alone in dealing with this issue. My phone is admittedly an older model, though certainly not ancient - it's an SE (2016). Nonetheless, this phone was perfectly viable on iOS 13. Ever since installing 14, it has been borderline unusable unless it's plugged into a wall, and with the latest update, it's been extremely dicey EVEN while plugged into a charger. It will charge to 100%, then immediately crash, sometimes powering up to 1%, sometimes (and most troubling) not powering up for several hours. This is f*cking ridiculous. I might as well go back to a landline. Please undo this update until the bug is fixed.