Are there permanently mounted bike computers?
To err is human, but to really foul things up you need a computer.
  
  Paul R. Ehrlich


The best computer, is no computer at all! I am sure I will take flack for this, but if all you are interested in is speed and distance, why not go with an old style bike speedometer.  Permanent mounting and no batteries.  Just watch out for the roaming bands of bike hipster thieves, they may steal your whole bike to get at the speedometer.