Depends upon the camera. I have a Bessa R3M, with a 35mm f1.4 lens on it. I travel a lot on business, and this camera can drop into my briefcase or coat pocket and give me something to shoot with when I am away from home (I usually shoot 4x5 which doesn't fit in a pocket). The R3M has a battery to power a meter, but operates just fine (albeit without the meter) without the battery.
Originally Posted by Colin Corneau
The 'A' cameras need the battery for the shutter, and are therefore more dependent upon the battery - but the batteries that they use are small, and it's easy to carry a spare.