Has anyone tried mounting a trolling motor to their kickboat? If so, what kind of battery would you use? The deep cycle marine batteries seem too heavy, would a smaller battery like a motorcycle battery work?

I'd go with a smaller sized deep cycle for more sustained power. Especially over the course of a long day or two. A motorcycle battery is good if all you're running is a depth finder and a bilge pump for your livewell. Of couse you'ld have to have a kickboat with enough stability to support the weight.

How long the battery last will vary radically with the type of trolling motor you get/have. I used to use a older style Minn Kota that had 4 forward and 2 reverse speeds. The way it ran slow was by throwing away most of the battery power -- 10% speed meant 90% waste (probably not quite that bad, but it bit). My newer trolling motor is also a Minn Kota but has infinitely variable speed. It uses pulse width modulation to control speed -- it effectively turns on and off really fast with more on time for higher speeds. The results are tremendous. Not only do I get fine control over the speed (the lowest speed on the old one was usually too high for my 12ft aluminum boat even with 2 guys in it); I usually run the new one with the prop turning between 2 and 5 revs/second assuming calm water and no significant wind. On top of this, a battery seems to last about 4 or 5 times longer -- i.e. you could get a way with a smaller battery. You still need 12V though and a battery that can provide significant current (amps) without the voltage dropping off, you just don't need it to have as much total amp/hours of storage.

I can't over state the need for infinite variable speed on anything that can drift easily. Actually I'd never use anything less on any boat.

One other thing to keep in mind is that deep cycle batteries have thicker plates and last a lot longer when going through deep charge/discharge cycles. Other batteries are heavily stressed by deep cycling and will wear out in far fewer cycles.

I use a standard "car" sized deep cycle battery in my boat to run my trolling motor, sonar, and gps. Granted it is heavy, but not nearly as heavy as the "truck" sized ones most people use in bigger boats.

Oh yeah, one other thing about running an infinite variable speed trolling motor from the same battery as your sonar... you may need to add a fused ground lead from the negative terminal of the battery to something conductive that goes into the water. I didn't need to do this with my old humminbird sonar, but when I upgraded to my Lowrance X85, I was getting noise on the display from the trolling motor. Added the fused ground path to the water and the noise is gone.