Battery problems on MacBook Air I have a 13" mid-2012 MBA, which runs fine except one thing: in the past year the original battery started to deplete its charge quickly and now only holds about 50% of the original capacity. 

So I decided to buy a new battery and bought one on eBay from as seller with extremely positive reviews. I replaced the original one and was happy for a short while - everything seemed great. 

From time to time my Mac stops seeing the battery and I get a "no battery available" status and a X on the battery icon. Sometimes it goes away by itself after a fairly long time, once I had to replug the battery for this to go away. When I see this warning, mac goes to sleep immediately after unplugging it.

Is there anything I can do about it? SMC reset doesn't help.
You should only use the original Apple battery. You can read everywhere that cheap other brand batteries are s**t and go broke very soon or immediately. (The same goes for batteries for cameras).
Perhaps you can recover your money from Ebay.