Gift card balance
How do I find the balance on an apple gift card.
The actual gift cards can only have either the entire value they state or 0. Once redeemed, the entire balance is transfered into the Apple ID that redeemed it and the gift card itself is empty.
To find out if the gift card is empty or not you have to try and redeem it.
Otherwise, to find the balance on your Apple ID, follow the steps here: link-> Check your Apple ID balance - Apple Support