https://www.amazon.com/dp/B01FF1XJX8/ That one lasted December through August this past year.

Now I'm trying this one: https://www.amazon.com/dp/B01LXCS553/

Fulfilled by Amazon (FBA) doesn't mean a thing about product legitimacy. Any seller can send their products to the Amazon distribution centers and Amazon will ship for them. The only thing FBA tells you is that the item will ship from an Amazon distribution center.

Even worse, if multiple sellers offer the same item, there's no guarantee that the item you buy will have originated from the seller you choose. Many FBA products have commingled inventory, where all the different sellers' items are stocked together instead of being sorted by individual seller, and Amazon will ship you any seller's item out of that combined inventory.

The rule of thumb with Samsung phone batteries is to avoid the ones that claim to be made by Samsung, because those are the most likely to be fake. Instead, get a reputable third-party brand like Anker that is sold only by that company (whether fulfilled by Amazon or not). There are a couple of other brands I've seen recommended too.

Here is a link to an Anker battery on Amazon. The new kind.

https://www.amazon.com/Anker-Replacement-Battery-Samsung-T-Mobile/dp/B01LXCS553

They don't have the two pack deal anymore, but still pretty cheap for a phone battery.

As far as the difference, no idea. My Anker batteries have been very good to me though. Last all the way down to 1%