i have similar experience with NITdroid...

more then 5hrs of On-screen(continual use till battery cry for recharge) time and 4hrs on wifi hotspot... more then 15hrs on normal use...
and it was cold too as you mentioned

the reason i felt for it was 'heapsize' which was not set by me so it ws '20m' only & no swap...

after changing both of them i.e heapsize to '36m' & enabling swap.. NITDROID BECAME A MAMMAL i.e always hot & hungry
this is what i observed, it might be wrong

so is there a similar concept of heapsize in maemo too