Beats Studio Wireless headphones not charging.

I finally found a charger for my headphones after years of not having one (got them from a friend who lost it) and when I plug them up to charge I get a blue light with a slight red flicker. After hours of being plugged up they haven’t charged at all. I want to look into getting a new battery for them but don’t know how to access where the battery is or what battery I’d be ordering as a replacement. Any help? It would be greatly appreciated as iPhones don’t have the same headphone jacks as I need and I really like these headphones.