Is it normal for a 7th generation iPod nano to heat up while charging?

Hello everyone, last year I bought a 7th generation iPod nano. However, I unboxed it last month because I was abroad for almost a year. So I unboxed it as soon as I came back from abroad.

On the one hand, a while ago my ipod was charging and there was a time when I touched the back of it with my hand, it felt warm. Then I waited for a few minutes to touch it again to see how it felt that time and when I did it, I also held it for a few seconds and it felt like it was heating up.

I almost forgot to mention that the day before yesterday I was listening to the radio on my iPod when the battery was low. Whereas, the battery icon eventually turned red indicating it was less than 20 percent charged and it would need charging soon. I kept on using it, despite it showing the red bar.

Almost immediately after the red bar showed on the screen, the device started getting kind of warm while I was holding it (especially the back of it).

My question is: Is it normal for a 7th generation iPod nano to heat up when it's charging and/or to feel kind of warm when it has a battery level around 20 percent or less?

Anyway, I plan on calling apple technical support tomorrow to ask them if that's normal and because it's going to be out of warranty on 19th this month.

Thanks in advance and sorry for my ignorance. This is the first time I own myself an apple product.

I apologize for my english. As you can see, it's not my native language.