How to choose mac battery?
Apple does not sell or distribute its OEM parts to consumers; Apple parts are only available to Apple stores and to Apple Authorized Service Providers. To get an Apple battery, you must either take your MacBook in for repair at an Apple store or to an Apple Authorized Service Provider. Neither of these sources will sell parts (here, a battery) by itself.

Thus, all MacBook batteries offered in the marketplace are non-OEM. They may be perfectly good (perhaps even taken from the same factory production line as Apple's parts), or they may be inferior. 

As a consumer, the best you can do is to buy from a reputable source; one that offers its own warranty, and will replace the part if it is defective.

I've installed several MacBook and iPhone batteries from iFixit.com, using non-OEM replacements. They've worked fine.