Traction batteries in a steel case are 24v and up. Adding 24v to 36v would make it difficult to properly charge without going high on the inverter.
At work we found out the hard way that you have to get a 24v forklift stack up to at least 30.6 for a minimum equalizing. That means 45.9v for a 36v stack, 61.2v for a 48v stack, and 76.5v for a 60v stack.
The SW4048 input upper limit is 66v. The safest forklift stack you can operate on the Trace is a 48v nominal.
If you can find a 24v 1000ah traction battery with a bunch of bad cell, you could rewire it for 12v and add it to your Deka.