Battery issue

I am using iPhone 11 from the last 8 months. From the last 2 months I was facing an issue regarding battery. My phone can not charged more than 80%. It stuck at 80%. I got the support from the care, they told me to put it in a cool atmosphere for getting 100% charge. I charged my phone under the cooled temperature. But it can't charged more than 80%. And after using 5-10 minutes phone's display was getting warm.