new ipod 7th gen battery seems die fast

I bought a new ipod classic a couple days ago and I have done all the step apple said to enhance the battery life. When im playing music and the life bar seems that it is loosing charge pretty fast, like playing music for two hours and the charge looks like about 80 % and that doesnt seem logical, I play my music volume at about 70 to 75%. And my headphones are big headphones, but someone said that it doesnt matter when it comes to battery life.

Any info would be helpful.

Thanks