The regular trolling motor will use the same amount of power from battery regrdless of power settings. In order to make battery last longer on lower settings you need to have a motor capable of switching the current on /off. Minnkota maximizer technology or Motor Guide Digital variable speed control are the features you need to look for in the motor. The basic low end motors do not have them. From my own expirience extra price you need to pay for the motor is well worth it.
Life is what happens to you while you're busy making other plans. - John Lennon