All the reading that I have done on electric propulsion, lately,, indicates that better efficiency is gained at higher voltages. Your friend is likely running those 6-volt batteries in series,, ie: 6x16=96volts. My books recommend 120v systems, preferably 6x20 batteries=120volts, or alternatively 12x10batteries=120volts. Battery techologies will improve dramatically, now that the big automakers are scrambling to develope this sector. But the real heart of any system is the controller, and there are some excellent regenerative options already developed,, just waiting for market demand. The next 5 years should be a very interesting time for this stuff.
Alan