|Click show for a short list of the current PHEV conversion and kit options for the Toyota Prius.|
This item is out of date but kept for posterity sake,
This is where you will find Battery Options for various Prius PHEV conversions.
- See Current Prius PHEV Battery Options
Original CalCars Method
This information applies to the Original Prius PHEV#CalCars Method which did not utilize the stock NiMH battery pack. Further development of this method has been postponed while exploring the new Prius PHEV#Hybrid-Pack Method.
Any battery which meets the minimum requirements could be used to replace the Stock Prius battery pack. The stock battery does not necessarily need to be removed, but should be disconnected while in PHEV mode due to serious problems that can occur from paralleling this sort of battery. Adding more than 300 lb to the vehicle's weight is not recommended, at least without beefing up the suspension; removing the OEM battery pack removes around 80 lb.
This application is on the edge of the capabilities of lead-acid (PbA) batteries. CalCars' PbA conversion works, but just barely. The battery pack's internal resistance, though O.K. at high states-of-charge (SOC) is twice as high at low SOC. As this is what ultimately limits discharge, it also means that ordinary hybrid operation is compromised, too, once this low SOC is reached. Additionally, and possibly most important, low temperature operation is very compromised. Range is reduced at least 20% at 50 vs. 70+ degrees F, and at freezing temperatures CalCars' PRIUS+ wouldn't drive at all on the PbA pack!
- CalCars has used 18, 19 (most rescently), or 20 EVP20-12B B&B 20Ah 12v SLA PbA batteries from ElectricRider.com (~270 lb and 12Ah at 2C rate) for a total of 3.1 kWh. These PbA batteries have exceptional high power capabilities, cost $750 total, and deliver 10 miles of pure EV driving or 20 miles of doubled gasoline mileage in mixed driving per charge. CalCars' first set lasted 200 cycles or $0.35/mile -- but see RonG's further information under Charging below.
- Another PbA possibility is the Odssey PC625 by EnerSys Inc. They are slightly lighter for the same high rate capacity and may have longer cycle life than the EVP20-12B. I believe these are what used to be the much-touted Hawker brand. More info on these batteries, where to get them, and for how much will be forthcoming -- and, again, see RonG's further information under Charging below.
- CalCars has nearly completed a project with Electro Energy Inc. using a custom pack of their specialized NiMH batteries. Though more expensive, it will weigh the same as the EVP20-12's but provide more than double the range, better performance, probable low temperature operation, and much longer expected lifetime. We are hoping that Electro Energy will make these available for conversions later this year (2006). Stay tuned.
- EDrive plans on using 18 exotic 12V U-1 U-charge 40Ah @C/5 Li-ion batteries from Valence for a total of 9.9 kWh.
- Useful files by Ron Gremban:
- You may want to use some Anderson high power connectors for the DC connections. 
We will focus on the Voltage requirements, as the AmpHour capacity of the pack may vary depending on who's implementing it and for what type of useage for various ranges from 5 to 50 or more miles. While a PbA pack may only deliver about 1/2 its nameplate capacity (due to Peukert's Law, which does not affect other chemistries) a Lithium pack may be able to deliver all of it's nameplate capacity. It all depends on how the battery's capacity is rated. The Prius consumes about 1 Ah or 300 Wh per mile.
- The 6.5Ah Stock NiMH pack consists of 168 cells (28 modules) in series.
- 60% nominal to 45% minimum SOC => 15% of 6.5 Ah is 1 Ah for 1 mile EV-only range.
- 80% maximum to 45% minimum SOC => 35% of 6.5 Ah is 2.2 Ah for > 2 miles EV-only range.
- Nominal Voltage is 201.6V, ranging from 180V to 270V durring use.
- The 20Ah CalCars PbA pack (12Ah at 2C rate)
- Delivers ~10 miles EV-only or 20 miles Mixed-mode driving PHEV range.
- Nominal Voltage is 216V, still ranging form 180V to 270V durring use (range set by Toyota's hybrid system).
- The 40Ah EDrive Li-ion pack
- Delivers ~30 miles EV-only or 60 miles Mixed-mode driving PHEV range.
- Nominal Voltage is 230V.
CalCars' published chemistry-neutral PRIUS+ battery spec is reproduced below. We have found 18 12V PbA modules or 180 NiMH cells in series to be near optimum. In rescent CalCars PbA conversions 19 12v modules are being used instead of the earlier 18, some testing has also been done with 20 batteries.
Note: our PRIUS+ gets approx. 1 mile of pure EV range (or 2 miles of Mixed-mode driving range, with double normal gasoline mileage) per Amp-hr expended from the battery. Therefore, a 30Ah battery, used to 70% depth-of-discharge (DOD) would provide 24 miles of EV-only range or 48 miles of Mixed-mode driving PHEV range.
- California Cars Initiative PRIUS+ Project - Preliminary Public Chemistry-neutral Battery Pack Specification
- Subject to Change 6/17/05 By Ron Gremban
- Maximum (during regenerative braking, 120A or max for SOC): 260V
- Minimum (during 120A discharge at minimum normal SOC): 180V
- Nominal: 210-230V (depends on the chemistry)
- Amp-hr at 60A rate: 30-50 (5.5-10.0 kWh)
- Max intermittent discharge rate: 200A
- Max intermittent charge rate (when SOC is low enough to accept this full rate): 120A
- DC internal resistance*, over normal range of SOC: Less than 0.25 ohm (0.20 ohm desired)
- Charge equalization: Please indicate requirements and provisions for charge equalization
- Thermal management: Please indicate requirements and provisions for thermal management
- Min cycle life*: At least 1000 cycles between normal SOC limits; 2000 cycles or more highly desired
- Max battery pack weight*: 300 lb (136 kg); 170 lb (77 kg) desired (replaces 70 lb hybrid battery)
- Max price*: $800/kWh or less to CalCars, including charge balancing, cooling, thermal management, and SOC monitoring
- Projected high-volume auto manufacturer's cost in two years*: $0.40 or less per kilowatt-hr lifetime throughput
- *The values of these parameters should be maximized (or minimized, as appropriate), given a reasonable cost of doing so
Battery analysis by Richard
I have completed my analysis for the battery pack and am attaching it. The first attachment explains the analysis and the second is a spread sheet of some of the data I ran.