It seems that two years is about as long as the NP-FS11 batteries last, as shown by the two lower curves from the ones I rebuilt in December 2013 with cells from 2011:
The two middle curves with those same colors show the “back then” performance of those batteries: they’re shot in both total capacity and terminal voltage.
I bought enough cells back in 2011 to leave two cells unused until now, which I built into a pack and charged. The green curve in the middle shows the result: those cells haven’t lost anything over the last five (!) years, as their performance still matches the other two batteries when they were new.
The red curves come from a pair of batteries made with fresh new cells from batteryspace.com. They’re nominally 650 mA·h cells, so the NP-FS11 configuration (two parallel cells) should produce 1300 mA·h; surprisingly, they show 1500 mA·h with a nice voltage curve.
So, although the 2011 cells work as well as their (now defunct) siblings, that pack can’t deliver the same capacity as the new cells. I expect I’ll rebuild it with 2016 cells in about a year.
For whatever it’s worth, rebuilding these batteries goes much faster when I don’t have to saw them open. The Kapton tape wrapped around the case halves secures them well enough; there’s no need for fancy gluing.
Yeah, I should make better labels. It’s hard to form a deep emotional attachment to the poor things, though.
Here’s a case where something performs better than expected; I don’t always buy cheap junk from the usual eBay vendor…