We built this unit specifically for locomotive.
Product & Voltage:
Loco-72: 72 volts with Capacitors - Starts large trains under the harshes conditions. 
Dimensions: 30" x 48" x 24" 
Weight: 600 lbs
Cable Size (American Wire Gauge): 
0000 (4/0) 
Cable Length: 
50'
Cable Termination Option:
Quick Disconnect (yellow) / Copper Parrot Clamps (1000 amp)
Features:
Patented Smart Start Technology
Polarity Protection
Ultra Capacitors
Marine Grade Digital Voltage LED Display