24 volt electric heat problem

[David_T]

I would be very suspicious of the current requirements of a forklift motor. Does the motor have four wires? If yes, you are wasting power with a field winding. You need to use a permanent magnet motor ( two wires). Are there any ID plates that tell the motor specs?
After determining the current draw, there is the question of your batteries. What is their capacity in amphours. I personally do not like deep cycle batteries that have any cold crank ratings attached to their description. Just a number like 60 amphours, 105 is much better. This number is how much current is available for use before the battery is "dead". Go to a battery makers website for lenghty explainations of ratings.
I also suspect your system is not providing regenerative feedback, which will recharge as your coast.
How old is the second original battery? Always bad to mix batteries of different ages.
Once you determine the amperage draw of your system, example 18 amps, you divide it into half of you battery capacity. YES--half! Deep cycle batteries are much happier if only discharged to 50% before recharging. Give you a ballpark time figure for operating.

[ERSwain]

Thanks for all the comments and suggestions. I have posted a picture of the board that I put in there. I have not motified it in any way. I does have 4 wires going to the motor but I cannot read the label on the motor. Both batteries are new and are deep cycle. Since this engine isn't meant to go extremely long distances, I didn't purchase the expensive batteries to go in them.