So ever since I got my iphone 4 I have been doing everything I can to retain as much battery power as possible, this included keeping 3G turned off and Bluetooth turned off. Well this week I decided to leave both 3G and Bluetooth turned on just for the sake of seeing if it actually uses more power or not. (yes, I fully understand that when you are using 3G and bluetooth the power drain is quite apparent, however, I am not using either of these. I simply have the options turned on, but when I am at home, I the wifi is automatically the priority, so my phone uses that for data, not 3G, and I am not actively turning on any bluetooth devices, so my bluetooth is not active, just simply turned on) so far it seems to be pretty normal battery usage. Nothing more than what I normally use on a daily basis, so I think I will be fine leaving both options on.

My question is, however, I want to leave tethering turned on on my phone, rather than turning it on every time I want to use it in the settings menu and then using it. I have tried to rationalize and put together a convincing reason as to why, but honestly it's simply a combination of laziness and liking the idea of just plugging my phone into my computer and then going to a website, even though realistically turning on the option manually each time really, really is not that big of a deal. Will leaving the Tethering option on drain any more battery power from my phone at all?

I have my mac network settings to have the network options set to Airport, Ethernet, iPhone and Bluetooth Pan (plus the other two, both of which I never will use because I don't know what devices/options Bluetooth DUN uses and had no idea you could access internet over firewire, so I would have no idea how to get that going either) and to people who don't use Macs, basically that just means that the computer sets priority to network access methods, so it by defaults always accesses internet over AirPort, but if that can't be found, then it looks for Ethernet connection, and if that can't be found, it then accesses internet through my iPhone via USB, and if that can't be found, then finally it accesses internet through my iPhone via bluetooth.

I know my computer won't accidentally access the internet through bluetooth on my phone if any of the other internet sources are present, so I'm not worried about the phone draining power that way, but I do understand that internet via bluetooth would use power obviously. But, if my computer was not connecting through my phone to the internet, would simply leaving the tethering option left on drain more power from my phone, or is it just like 3G and bluetooth where the option left on causes no drain, just use of that particular connection causes power drain? I hope all that made sense! Thank you for anyone that can help!