I just tried out a 23 turn double motor that I installed in my Profisherman Bass Boat. I have 2 identical 7-cell NiCd battery packs that I'd just charged. One of them is new, the other a year old. I ran the new one first and everything was ok - run time normal, nothing too hot after, boat speed not noticeably different than with the stock motor. After half an hour I tried out the second pack. Right away something was wrong. The boat only had about half the power. I ran the pack down which didn't take long and noticed the plastic had melted away from one of the cells in the pack. At first I thought the problem was with the battery pack but now I'm wondering if the problem was something else which caused the battery to overheat. I measuered the battery voltages before and after the runs:

new battery before=9.93V after=9.02V
1 year old battery before=9.66V after=9.09V

Any ideas?

Another thing. The steering servo has stopped working but I think this is unrelated. At the end of the second run the boat was full of water. Maybe it will work again when things dry out.