Ah, so this is what a frozen battery feels like

[That_Prius_Car]

I have operated my Prius in -3 degree weather before, it was a bit less powerful, and didnt use EV mode as agresivly

[BAllanJ]

Battery heaters are used in some parts of Canada where it gets really cold (-3 doesn't count... -40 does) as well as in car cabin heaters. They aren't for improving mileage. When a battery gets cold, the chemistry gets slower... less current from the battery and a harder to start engine. The cabin heater is just for comfort.

In some of those places, plugging your car in is not an option, because your coolant will freeze solid if you don't. If you can't plug it in, you have to leave the engine running when it's -50 C.

Now that I'm thinking about it...I wonder how a NiMH battery does at low temperatures.

edit... by plugging the car in, I meant a block heater, not a battery charger.

[BAllanJ]

OK, so I typed that before I read the old part of the thread.... We don't often get colder than -30C here, so I suspect I'll always get a bit out of the traction battery. Hope it's enough to start the ICE. There's a trick I've used on other cars when the battery was too cold to turn the engine over.... turn on the headlights for a minute, then turn them off and start the car. The current pulled through the internal resistance of the battery warms it up a bit, so then you can get more current out when you turn the key.

NOw I'll have to think about how best to apply that to the Prius...

[Bob64]

The prius should always have enough traction battery power to start the engine no matter what temp it is outside...

[Ct. Ken V]

Hi, BAllenJ,

I don't know about your claim of "internal resistance warming the battery" by turning the headlights on briefly. I was told years ago that turning the lights on & off first was to de-gas (remove the bubbles from) the plates so more electrolite can make plate contact to produce more current. That had always made sense to me, but it may not be true. Maybe YOU are right. Anybody out there with some electrical knowledge of batteries that can confirm one or the other theory?

Ken (in Bolton,Ct)

[BAllanJ]

Originally Posted by Bob64

The prius should always have enough traction battery power to start the engine no matter what temp it is outside...

I know it has enough energy, but if the chemical reactions slow too much due to the cold, there may not be much power. Like I said, -30 C is probably not too much of a problem.

Regular dry cells, like your duracell AA for instance, are pretty useless below -20C.