Motorguide brute problem

Just bought an used Motorguide Brute model no.. 765 Duraamp II 24v foot control. It has variable speed thru a rheostat. This morning was the first time I took it out with fully charged bats. It worked perfect for 10 minutes then the variable speed rheostat stop responding The motor works in high speed bypass, but when i try to run it thru the speed control rheostat it stays at very low speed. It will adjust to off and very low. Anyone know what has happened. I did some searching and found a post where the rheostat was replaced but it didn't fix it.

SOLVED .
I checked the batteries and one had 8 volts. So I put a good battery in it and it works like new ;)

Well we fixed that one for you. Just joking, glad you found the problem.