Anyone know a trusted source for EP121 batteries?

Trying to revive my tablet. Recently got into Tabletop RPG's and needed something portable for carrying around the massive collection of PDF rule books. It seems its been sitting in the closet for too long and the battery is completely dead to the point of not even charging. Called ASUS they were kinda dickish about the the whole thing claiming couldn't sell the battery without sending the unit in. Found ALOT of listings online but frankly a lot of them were sketchy. Can anyone recommend a good seller where I can find batteries that can be trusted to be OEM or at least aftermarket of acceptable quality. I just don't want a counterfeit exploding in my lap and its really hard to find legitimate listings these days.