Apple 11" Intel i5 64GB SSD MacBook Air

Who did the refurbishing? Was it manufacturer refurbished or a re-seller?

This was not refurbished by the original manufacturer.

Is the battery made by the manufacturer or is it an aftermarket battery?

Because these items are refurbished I cannot say with certainty if your order will contain a manufacturer original battery or not. Each item will have undergone various degrees of renovation.

Can it be upgraded to the current mac os version?

Dealbreaker.

http://i.imgur.com/ELKNQUI.jpg

I just received mine yesterday and upgraded to El Capitan without any problems.