How much does it cost to have the battery replaced in my iPod Nano Ver7?

The iPod nano 7th Gen is now considered vintage and I don't believe Apple provides service for it any longer. I have included 2 support articles, the first one is about obtaining service for obsolete or vintage products and the second one is Apple Support page for the iPod.

Obtaining service for your Apple product after an expired warranty - Apple Support

iPod Repair & Service - Apple Support

I’m not sure Apple will replace that battery but you can contact service in the link below. Select Get Service.

iPhone Battery Repair & Replacement - Apple Support