Within 4 hours of turning the heat up, cell no.10s output bottomed out at around 217mv 0.78ma cell temp ~ 18degC, then fairly rapidly began to rise.  Two hours later at around 10:30pm we're reading 230mv 0.82ma, cell temp holding around 18degC.

It's close to 11pm now, no.10 is bouncing off 0.83ma at 231mv.

The morning expects some kind of surprise, for certain.  

This is one of those moments where automated continuous data logging would be amazing.  The graphs would certainly look a lot prettier.