AirPods charging case problems

Hi Avery here I live in Nigeria but got AirPods as a gift from someone In the US.so prior to use I noticed the charging case doesn’t charge but the charging cable works fine on my iPhone.so basically I tried all the troubleshooting ideas nothing worked .i would be in the use soon and I know my warranty is still valid ..my question is I don’t have the proof of purchase cos it was a gift so would I still be able to use my warranty regardless?two and does my warranty cover that cos the damage is not from me