My Sprint.com info also still shows a $12.95 credit. If it sticks, cool.
I'm not 100% sure about this, but usually, Sprint will take the money they charged you and put that as credit to your account. They then bill you for the battery making the credit go away.
(the $12.95 amount is what is confusing - is that all that Sprint said they'd charge you? Or did they authorize $14.xx? If so, you may have gotten lucky and will get the credit for shipping! wow!)
I see a credit for $14.xx on my sprint account which I'm expecting to vanish once they bill me for the battery