[Chadfrom308]

The CNC Lathe at my work has a 20hp vector drive amplifier that powers a DC brushless spindle servo. The problem is that it takes 3 phase 240 volt ac power and cost $5,000.

In realistic terms, maybe try getting as big of a battery as possible? maybe a car battery or a really big lipo (very expensive)?

The thing is, batteries running out of juice isn't necessarily a bad thing. The motors get really hot (especially because they are hauling a 150lbs robot around), the compressor needs to catch up (it only has like a 20% ish duty cylce) and it can give you a way to take turns.