Although electric hybrids are well proven, electric hybrid technology is limited in several ways:

1. Cost.
   The cost of second generation batteries that can charge faster, go farther, and last longer are currently prohibitively expensive, ranging from $10,000 to over $40,000. Many battery systems are rated at 500 cycles—or about 18 months of daily charging before replacement is necessary. Equivalent hydraulic pump/motor and tanks cost $2,500.
   
2. Charge time.
   Charge time not only impacts overall efficiency and utilization, but also how efficient the brake regeneration system is. Toyota currently estimates their brake regeneration system at 30 percent efficiency, while hydraulic brake energy regeneration efficiency is over 80 percent, since hydraulics are not limited by battery charge limits during the regeneration cycle.
   
3. Battery Weight.
   Weight has a dramatic impact on overall transportation efficiency, and even lithium ion battery technologies add significant weight, ranging from 350 to well over 1,000 pounds. Equivalent storage in carbon fiber tanks weigh 75 pounds.
   
4. Maintenance talent availability.
   Electric hybrid vehicles are highly complex and the DC power can be dangerous if not handled by specifically trained mechanics. There are not a large number of specifically trained mechanics in the US today, and the training requirements are significant. Most fleet mechanics already have training and a strong comfort level with hydraulic technology.
   

With the current electric hybrid limitations in mind, and recognizing that there are currently no competitors serving the light- and medium-duty hydraulic hybrid space in the automotive or retrofit markets, HHS has designed a Hydraulic Hybrid System for the automotive and fleet vehicle retrofit markets.