Hydraulic Hybrid Systems introduces a bolt on retrofit that increases MPG 40% prices start at $12,900. The demonstration vehicle is a 2002 Chevy 2500 HD. 

    At this point relying on a battery for anything more than auxiliary or low load applications will put you in a bad situation.  There are at least three reasons to not have an electric hybrid.

1. Cost of mining materials to build batteries. Whereas biodiesel can be grown batteries can not. Batteries do not grow on trees.   They are not biodegradable. By buying a complicated piece of machinery you are creating a job someone will have to clean up in the future. It is not sustainable to buy a car like you buy a cell phone.  We should move away from disposable vehicles. More Deloreans and Hudsons.    Otherwise auto mechanics will go the way of TV repair men. 

2. Low power density. Electric cars OK for people in the city. But people in the city should be riding something with rails not rubber wheels. 

3. EMF still need proof electromagnetic frequency is OK in hybrid vehicles.  

Here is what Hydraulic Hybrid System says about the subject:

The retrofit will be available by authorized distributors and installed by their mechanics to put on fleet trucks (it will not be available to the general public as a kit for probably another year or so.)

The starting cost of the retrofit is $12,900 and goes up from there depending on the size of the vehicle it will be put onto.  HHS's base unit retail cost of $12,500 includes the hydraulic pump/motor, high and low pressure tanks, transmission coupling and the controls.

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. Chevrolet has rumored that the Volt battery pack currently costs more than $16,000. Tesla has indicated its battery pack is over $40,000. Both 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. Toyota’s current battery pack adds 150 pounds to the Prius, the Chevy Volt battery pack is expected to weigh 350 pounds, and Tesla’s battery pack exceeds 1000 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.