This belt is from a small wedding videographer's stock.  There are no batteries with this unit, thus the low price.

This is from the NRG Brochure:

This 4.9 lb. wonder is our most popular power product and is relied on daily by thousands of videographers the world over. From the serious "prosumer" to the full-time working professional, the Power-Pro+ is the basis of a sophisticated and affordable power system that can be expanded as a user's needs demand. The Power-Pro+ belt is a unique combination of power and comfort. 

It features:

• interchangeable high-capacity, memory-free, quick-charge-capable sintered Ni-Cad power packs
• Power chassis with dual inputs
• Battery pack change without shutdown
• Dual power outputs for powering two devices simultaneously
• 5-stage multi-color "Fuel Gauge" indicator
• Auto-reset overload protection for connected equipment.