I don't think you can return just the battery. Besides, you really need at-least two. I had 6 before I started buying the new ones and found myself running out of juice on occasion.
People swear by the ocotominer boards, but I like more cpu and prefer to keep my rigs to 6 gpus. Right now I'm running these https://www.newegg.com/p/N82E16813145016?Item=9SIARTEFNN7753, but they use 6-7th gen CPUs. Super easy to setup and they've been solid.
I just ordered one of these...