Feasibility of Additional Batteries and Plug-in

Unless you are looking for an expensive hobby, wait for the plug-in model to come out.

Tom

 

The percentage around here is not large, if you are interested try a Google search on plug in hybrid conversions there are several available.

 

:nerdut a trailer h\itch on it.

 

Remember that, without modifying the program, no matter how big your battery will be, you can only drive 40mph and below. Beyond that speed, the ICE kicks in no matter what. That is why the Plug-In model that Toyota is working on allows up to 60-65mph. One of the challenges is on the heat issue of the electric motor.
My advice, wait for Toyota's Plug-In.

 

Its still pretty cutting edge, I believe there are only 70-80 in the world at this point.

You can find a lot of info here:
Prius PHEV - EAA-PHEV

The cheapest/DIY option is about $3-4k right now, thats the cal-cars open source PriusPlus conversion. Its basically a big 240V sealed lead acid battery pack, a 240V battery charger, a big switch (contactor) to connect and disconnect the secondary pack as appropriate, and a micro controller to monitor the car's CAN bus and determine when to open and close the switch for optimal performance.

The first commercial conversion that is somewhat affordable and has a warranty is the new Hymotion Li-ion pack at $10k:
Hymotion :: Enabling the new generation of hybrid owners to maximize their fuel efficiency

I'm in exactly the same boat, I bought a rebuilt salvaged Prius with the intention of eventually converting it from this guy:
Plug In Hybrid Electric Vehicle PHEV

Rob

 

While 60 mph EV mode would be nice, its not as big a deal as you would think. When you maintain the oem battery SOC at a very high level the HV controller tends to use stealth and warp stealth modes a lot more often. It also tends to use more electric even when the ICE is powering, which is where the ~100mpg sort of numbers come from.

I would agree that conversions may not be financially rewarding, but if you enjoy the technology and value the reduction in fuel consumption beyond just its retail price tag there are some pretty exciting options starting to pop up.

Rob

 

You know the argument that the PHEV conversions don't make financial sense gets less every day. Gas here is the SF Bay Area now averages close to 4.60 per gallon. If you drive 15,000 miles per year and your gas mileage goes from 45-50 MPG to 90 MPG you will save about $1500 in gas cost per year - and that is at today's prices. Unless our government steps in to regulate gas prices, there really is no reason for oil companies to reduce prices. That puts the Hymotion pack at about a 6 year payback using today's prices. The Hymotion pack is expected to last for about 10 years, so you would already be ahead. Of course all of this is speculative as we really do not know where gas will go and do not have any long-term data on the Hymotion product.