Yeah, I'm not to sure how well this is going to work. I never dreamed the first cell in the set would last 10+ years. I'm quite interested to see what I have after so long. It's a standard food freezer with a defrost cycle. Don't know how or if that might have affected things.
I'll probably move it to the regular refrigerator for a few days for a slower thaw before leaving it out in cool basement for a few more...
That is a real mercury battery, the holy grail for us camera enthusiasts. It's clearly a mercury battery because the code is "675 PX". If it had an "A" or an "U" then it would be the alkaline. I own two such Varta cells and they are identical. And they are healthy still today (2015).
Why would this possibly be a "holy grail"? I have a couple sitting around that still worked the last time I checked, and couldn't be bothered with them. A silver oxide cell with an MR9 adapter is the perfect replacement and the zinc-air hearing aid cells work just fine too.
I bought several last-production-run mercury PX-13 batteries many years back. They've been stored in our refrigerator since then. The ones I've pulled out and checked have been fine. I use them in any of my classic 35 film cameras that need mercury batteries.