I'm in the same boat, and I just lost one of my spare batteries recently.
Of my four batteries till recently, three have been Canons and one has been a CTA which I bought a couple of years ago from B&H.
Of the four, the only one that ever failed was a Canon, so when I lost one of them I looked for more CTAs, but B&H no longer stocks them.
A google search indicated that they are in stock from
http://overstock.com at about $12 each, so I bought four more, which came very quickly. Overstock still seems to have them, so I would recommend buying a few while you can. At that price, if one of them quits, its no big deal, IMHO.
Eric