How to choose mac battery? I had a problem with my battery(as I think). Actually I asked the question before about this issue here MacBook turning off suddenly

And eventually, I have decided to change my battery. I opened my MacBook and took a few pictures





And now I would like to buy genuine MacBook a1417 battery, by this search request I can find on eBay a lot of offers, but the question here is how to understand that this or that battery a really genuine(original) and I that I can buy it without any doubts? 

For example this two 

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F202630493472

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F202496878288

Both of them wrote Genuine, but price difference in around 10$... and anyway how can I check that this battery really good and genuine one?
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.