Try getting a battery from OWC since they've been providing support for Apple products for decades and they have official resellers for other regions. iFixIt is also another option. However, even though both of these vendors are reputable, you may still get a defective or problematic battery from them....they both will honor the warranties on the batteries they sell, just read the warranty details on their respective sites. Unfortunately the quality of third party Lithium batteries is extremely poor even when purchased from a reputable vendor....even Apple & other OEMs have trouble with the OEM batteries from time to time.
I personally would try for a battery from OWC.
You will definitely want to use Coconut Battery to monitor the health of the battery to make sure it is holding up so you can look into a warranty replacement if the third party battery appears to be losing its Full Charge Capacity (FCC) too quickly.
If you are in the US, then another possibility is Battery Bob. I've only purchased one battery for my old Logitech Harmony One remote from them and am very satisfied with that battery. I had seen reports that the original OEM battery included some kind of chip or something that the remote needed. Most of the batteries I found online appeared to be the same third party battery without any detailed information (many reports seemed to indicate they did not & many reviews indicated the batteries swelled). I found Battery Bob's site and liked how they provided a lot more details on their products and seemed to have good overall reviews, plus their battery appeared to be different from all the other sites...at least they identified the manufacturer of the battery. I've had this battery for over a year (maybe two) and it is still going strong and has shown no signs of swelling which many of the other batteries were known for. I have no idea what their Apple laptop battery would be like. I think this is the battery (brand listed is Empire Scientific so maybe you can research their reputation...no idea how well Battery Bob handles warranties):
https://www.batterybob.com/products/5949-apple-macbook-replacement-battery-ltlp-9288-56/
I dealt with a vendor which seemed to provide our organization with good quality Lithium batteries...seemed like an Apple OEM battery, but they did not sell to the general public and later stopped selling batteries, so it is possible for some vendors to acquire decent batteries, but I think it is hard for them to do so.
Keep in mind that Lithium batteries must be properly stored (temperature & even must be stored with a 20%-60% charge). The longer the battery has been on the shelf, the more likely its charge may have drained. These are the vendors I would use myself...probably would go for OWC just because I have dealt with them for years even though we have a number of their batteries fail prematurely (at least in my opinion....but so did Apple OEM batteries at the time).
If an OEM battery is available, then that would be the one to get whenever possible. Unfortunately Apple does not sell batteries directly to the public, nor does Apple allow anyone else to acquire & sell the OEM batteries. Any third party selling an OEM like Apple battery is most likely one which Apple declined to use for one reason or another. Some other computer manufacturers do seem to allow third parties to sell OEM batteries to the public.
