Sorry for the delay in answering, I was travelling.

To make it simple, Ultracaps coupled in parallel with batteries will act like a shock absorber, this means that the battery will not suffer under high current loads (amps) and the voltage will be more stable; this is very important when you have old or almost empty batteries. Furthermore Ultracaps are almost no sensitive at low temperatures.

Ultracaps are UL certified, and are used in Busses, Cranes, Metros and LRV's and of course in Forklifts; Still in Germany presented last year an Hybrid, diesel-electric forklift with ultracaps for the energy recovery.

If I remember correct ultracaps didnt pass / or have not applied for a U.L. listing

Tell us more how ultracaps work?