There has been several discussions on which fish detector to buy that do not require a lot of battery.  It is known that most of the gray scale detectors require less power.  Most of the detectors on the market now are color and people have had trouble finding new non color detectors on the market. Two of the monochrome detectors on the market now are Lowrance MARK-4 and the Garmin echo 100.  I have not tested either of these detectors.  If you know of any other non color detectors please post their make and model and if you have any of the mentioned detectors a review including current draw and battery life.