It's not too hard to imagine that people who make the cultural leap to wearing Google Glass would be averse to adding the geeky pager-sized battery pack that will give them days of operation. I reckon your relief will be short-lived.

Even if the battery were comparable to a phone, the battery life would be measured in minutes if you left the camera on and recording all the time. The camera is the single largest consumer of battery on your phone (when in use).

If you don't want to believe the impracticality of it, than just look at the pointlessness of it. Why waste pointless amounts of battery, network bandwidth, and heat dissipation, when the data gathered won't actually help increase ad revenue over and above using GPS, search, email, and other activities as a proxy for your interests.

The idea that they need to know what you're looking at to serve ads just doesn't make much sense.

In addition to the short battery life, glass also get very hot when recording. It gets to the point that it hurts to wear after only a couple of seconds.