I guess if you actively using the BT, like a BT keyboard or BT headphone ie., the BT has to continuously check the status, I think they should drain battery. I guess my measurement on BT just leave it on may NOT be an accurate reflection of the power consumption. Here is my actual measurements, http://www.internettablettalk.com/fo...battery+tablet,
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If it is not mentioned, that means it is OFF, e.g. V+BT means only video and BlueTooth is on, all else are OFF, ie. audio/wifi are off.

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.......................N810..................N800. ...............770
Nokia menu........4.0......................3.5.......... .......3.0
To charge..........2.2......................2.2...... ............>8
V.....................5.8......................4.3 .................6.5
V+BT................5.6
V+w.................3.7
V+w+A..............3.4......................2.5
VV+w+A............3.1
VVV+w+A..........3.0
V+w...................-.......................4.1
V+2B..................-.......................6.1
V+4B..................-.......................7.3
mm+V+iGPS........8.1
mm+V+BT GPS.....-.......................7.5

Legend:
V.......... 1square of brightness
VV........ 2 sq of brightness
VVV...... 3 sq of brightness
A.......... 1 sq of audio
w............wifi
B............used alkaline batttery, not fresh
2700, 2000, 1800 are rechargeble NiMH of mAh capacity
mm.........maemo mapper 2.4.1-os2008, at leve 5, stand still, in a building
BT GPS....blue tooth GPS
iGPS........internal GPS
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bun