As Benson's pointed out this has been discussed numerous times in the past, but generally the consensus has been that whatever magical tricks the Nokia/Maemo guys have been pulling to make wifi-battery performance increases has also been applied to Bluetooth-battery improvements. i.e. back 770 days you couldn't leave your wifi connected and still expect to have a battery after a day, N800/810 improved this through hardware somewhat, but the big gains came as more recent OS releases (i.e. OS2008) added in much improved power management features, meaning permanent wifi had much less impact on battery life than ever before... same with BT, because at the end of the BT is simply a slightly lower power version of Wifi (the hardware is slightly different, but the principles of the radio are the same). So at the end of the day, if you leave BT on all the time does it hurt battery life? I would say based on what I've observed and read from others the answer is not significantly enough for you to care. i.e. using BT shouldn't cut your battery life in half compared to not using BT... but depending on what you're doing, if you say used a BT keyboard compared to just the hardware keyboard on the N810 for example, then you might loose, say, a few minutes of run time at the end of the normal battery cycle?... on the other hand, something like BT audio will actually add a few minutes of run time compared to taxing out the audio jack of the tablet because the BT audio device is providing it's own amplification power source.