ok this is what my friend in Nokia R&D said. No guarantees that 1) he knows exactly what is going on - he s not in N810 specifically 2) I did understand and deliver exactly what he said :-)

He mentioned a few leads:

- As General Antilles said, the battery is single stack so there is no adjustment of power consumption. However there are algorithms to optimize relationship between physical memory, consumption, and performance
- Introducing a new OS causes disruptures in the way the packages are installed because - according to him- the physical memory is not "blank". This can generate a "chaotic" usage of power until things get optimized.
- in stand by mode ( no application running, screen dimmed off) there are still a few things running. Did not say what.
- processor activity, Wifi and BT are the main causes of power drain.
- the battery time indicator in the status bar is not 100% reliable.
- he did not like the "heating up" symptom. Suggests a bug in the new OS that could/should be fixed by an update.

My n810 had again a seizure last evening. a few days in stand-by mode evaporated suddenly in a few hours. Found it in "coma", charged it up . Now showing 10 days, 7 hours.