U2 IC damaged, Phone won't turn on or charge. Altelnatives...?

I need some help. I got an Iphone 6S Plus that won’t turn on or charge. It was connected to a car charger and since then it’s damaged. I believe it is the U2 IC. And if I am right I’d have to replace the U2 IC right? but I have read online that the function of the u2 ic is to charge the phone when it is 1% or beyond, so if the battery of a phone would go 1% or under and it have a bad u2 ic it won’t charge but what about if the battery never goes under 15%? would I be able to charge my phone and use it if the battery doesn’t go below 15%? So if that is true I would prefer to charge the battery of my phone in another phone then put it on mine and never let it go below 15% then replacing the u2 ic which is a little complicated. Help let me know if this is true. Thanks