I’ve had a galaxy book alpha flex for the past 3 years and the battery is basically dead (barely 2 hours on max charge). I’ve seen some replacement batteries for sale on eBay and Amazon, but they all have wildly different prices and I’m not sure what to trust.
Laptop battery express is what I used for my laptop. They are a bit pricier than Amazon or eBay but they have better quality batteries and all their batteries come with a 2 year warranty.
Amazon and eBay batteries are extremely hit or miss.