Hi all,

I'm new to the site (great info, btw!), and interested in purchasing a Prius. Like many of you, I've experienced the same lack of knowledge from the dealer and find that I know more about the Prius than they do! My main concern is that the life of the batteries may be prematurely shortened due to extreme cold. We routinely experience -20 degree (sometimes colder) winter nights, and do not have a garage where the ambient temperature could be kept a bit warmer. I realize that the gas mileage will decrease in the winter months due to longer warm-ups, etc, but worry the severity of cold will have an adverse affect on the batteries.

Battery techies, feel free to blast me with info, I can handle it!

Thanks,
Reese

I thought heat was the enemy... not cold. But Honda's throw a charge into the battery pack when it's cold.


Regards,

AS FAR AS I KNOW (I have a fair amount of experience with NiMH batteries in many applications EXCEPT hybrid cars!) extreme cold should not cause any permanent damage to the drive battery. Now, how your vehicle will deal with the low voltage and the "apparent" reluctance of the battery to take a charge (very high internal resistance) - only the programmers who created the firmware for your car can answer that!

If you can get the car going, and the charging system can ignore the poor initial conditions, the batteries will warm up enough on their own, both from charging/discharging and the warmth of the car itself.

Let us know . . .

Batteries deteroriate in hot conditions. Cold lowers their performance but when warmed they recover. For storage, batteries prefer cold over warm, cold meaning chilled rather than frozen.

Better off with a Hybrid in the cold.

More overall battery power with less dependence on individual cells to deliver the necessary power to start the ICE means much higher reliability as compared to a vehicle that relies on a small number of cells, such as any typical 12v car battery. A Prius doesn't use the 12v system to start the ICE, so there's much less chance of a failure to start when viewed from a probability of failure due to extreme cold (lowering the effective output capacity of each cell) when the battery is made up of more cells. There is another factor though, the reliability of the cell connections, and Toyota has addressed this in the Prius I, as a recall to clean and re-seal the battery due to some corrosion, so as long as the battery is properly sealed where needed when there's condensation it's fine, and I would assume they addressed this completely in the Prius II.

Also consider the efficiency of starting the ICE with an AC motor rather than a small DC motor as in a conventional car, and the likelyhood of a mechanical failure in the "starter" is much less, and found to be very reliable. Also consider that the high voltage DC is converted to AC, and in effect regulating the voltage as necessary, so the available power of the battery is not usually fed into the motor, so even at very "low" battery voltage it's possible to still crank out significant amounts of power to the wheels, but depending on how "low" the battery is the computer will not let you drain it that much, for it knows it always need enough to restart and keep the battery healthy.

In general a Prius will keep the battery within a healthy range of charge and discharge for optimum functionality, and the computer keeps track of everything so any early symptoms of battery failure are recorded and you'll be alerted, whereas there's no warning or monitoring of the battery in a normal car, except perhaps luxury mobiles, but I wouldn't know, not owning them. The batteries are also said to be lasting longer than they first predicted when they were introduced in Japan in the 90's. That's good news in general because since those initial batteries there have been significant improvements within the same type of battery, such as the large Prius II battery. I think they will last at least as long as people generally keep "new" cars for, these days 10-15 years is typical of the people that hold onto a car, and that what's being predicted, at this point for battery life of the first generation batteries.

2001 Prius Photos       2005 Prius Photos
'97 Prius Simulation Prius inner workings

In regards to the issue of cold weather and the Prius, I can only say that last winter when we had a stretch of sub-zero F weather here, my 2004 Prius II did have some sluggishness in taking-off that went away after two minutes or so. The transmission whined a bit, but I found that letting the car sit for about two minutes before taking off seemed to have solved it.

If you look at the back seat on the passenger's side, you will notice a vent toward the top of the seat between the main center section of that seat and the door. That vent is the air intake to the battery. Many of us think that the purpose of that is for cooling the battery. Well the reverse is true during the winter. As the vehicle warms up the cabin interior the vehicle is going to pull that warmer cabin air down into the battery compartment and as such the battery will be warmed by cabin air.

Now, in the summer the battery temperature control system relies on the cabin being cooled to a reasonable level so that there is air cooler than outside air to cool off the battery during that season.

So, the long and short of it is that your comfort in the car is also the battery's comfort level and as such you should "set it and forget it" with regard to your A/C. Do not hesitate to run the A/C in the winter and in the summer at a temp setpoint and let the car decide how to keep you comfortable.

It has been said:
Hybrid drivers come in 3 flavors, greenie, techie and cheapie. Pick any 2.
2005 Prius, Melinium Silver over gray, package 5 (AI)