heat = traction battery damage?

No, you need to keep the AC on. The batteries get their cooling from the cabin through the vent in the right rear passenger area. It pulls this cooled cabin air through the batteries and exhaust it out the back.

 

Well, look at it this way the $$$ between 45 mpg's to 51 mpg's over a year is aprrox $7 a month in fuel cost.

For $7 a month do I prefer driving in comfort and protecting my very expensive battery?

Or sitting in a pool of my own sweat not to mention how much damage your doing to the wiring in the cabin of the car.
An un dehumidified cabin tends to corrode active electronic connections over years of use. Especially battery connections. Thousands of connections in that cabin.

BTW, I don't believe the ac hits you that hard anyway. You probably need a new aux battery (how many times have you had to jump the car) or your coolant pump is on the way out.

 

Short answer: keep the batteries cool - you will be glad you did.

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NiMH batteries would likely last 20 years if they were at room temperature, but road conditions are not remotely that kind. Lots of hardware to prevent the charge from going under 40% - long periods of disuse insure battery problems. Of more concern on this thread: more than 85% of charge causes heat. That or a very hot summer day



While it's a Honda Insight, the basic concepts are the same. Note the Prius until 2003 used the same kind of battery. Only 20% of the area is the black box on the right with the batteries....the rest is three fans, transformers, a box to determing state of charge, another box to coodinate the gas and electric motors, 12/144 volt conversions.

In plain English, a lot of hardware to give the traction pack long life.

My two cents: Use the A/C, park in covered or cool places when you can. If you have a minute before driving, open the hatch and doors to vent hot air. Finally, I would not overrely on the electric motor. I realize Honda's IMA system is more frail and this might seem parnoid, but these cautions won't hurt your Prius.

 

If the computers think the battery is too hot they will run a fan behind the rear seat vent to cool it, then quit using the battery, leaving you with the (now sluggish) engine alone. The computer will attempt to protect the battery, I do not think their will be major damage.

But the car is designed to get cool air from the rear seat to cool the HV battery, so provide cool air to your rear seat, run the A/C.

 

Since the battery fan has no air filter it also helps to keep the windows up and recirc on at all times, to reduce the dust level inside the cabin. For discussion and examples see here:
http://priuschat.com/forums/gen-ii-...oubleshooting/82092-battery-fan-cleaning.html

 

OK, this is what we're experiencing, perhaps someone can tell me if this is normal.

Great gas mileage on highway (at 55 mph we are getting about 51 mpg.) We live in the country and have lots of 3 mile runs that bring that average down, but for this tank of gas (currently at the 300 mile mark) my average is 50.7 mpg.

We expected the gas mileage in the city to go up, especially in stop and go traffic. But city driving seems to pull our tank average down.

Three times in the recent past the following has happened.

Road condition: level

Traffic condition: completely stop and go. When going, we are only going 3 - 5 mph.

Outside temp: 85 - 95

A/C was on but not on auto just low fan.

First 5 minutes of stop and go, we get 100 mpg. Second 5 minutes, we get 45 mpg. Third five minutes the ICE won't shut off, even when we turn off AC. Checked the bar graph thingy and once it was down to 2 red bars, once it was 3 bars but still blue, the third time I didn't think to check it.

Within five minutes of getting out of the stop and go, the graph again shows 6/8 bars blue or 8/10 blue (I'm not sure if there are 8 or 10 bars in total but it was all blue but no green bars.)

I've got a used 2007 with 69,000 miles on it, so out of warranty for the main engine but the batteries are still in warranty (warranty issues are tricky for me, though, because this is a US car that was imported by its first owner into Canada.)

Is this normal? In stop and go conditions is the traction battery running down due to the a/c trying to cool it and then the ICE is coming on? Or is there something potentially wrong with the traction battery that I should get tested?

The regular 12v battery was tested at its last check-up (1000 miles ago) and came out fine.

 

Perfectly normal, and your assessment is exactly right. The AC runs off the hybrid battery, and because the car is very protective of the battery, to avoid over-discharging it will let the charge go only so low before running the ICE.

 

Jimbo, thanks for the assurance. We love the car but were worried about the high miles and the fact that we are third owner of a car just 3 years old. Still haven't found out what was 'wrong' with it. I have all the service records since it was bought and the original window sticker. It had some body work done on a fender just months after it was bought so I figure the original owner worried about it from that point onwards. The second owner was dying and wanted to buy a 2010 for his wife so she'd be all set after he died. Or at least that's the story he told me.

But whenever anything seems 'off' I get worried. So far the only things we've found is that the resume doesn't always work on the cruise control and the parking lights turn themselves on for a while for no reason when the car is parked (and can't be turned off no matter what we try, but they'll shut themselves off after 10 minutes of so.) I'm sure that's a wiring fault with the aftermarket installed daytime running lights (to make the US car legal in Canada) but I'm not paying anyone to go searching for an electrical glitch like that. Every once in a while, we'll see the garage lit up by the car. I can live with that.

 

This could overtime cause a problem with the 12V Battery

 

A ScanGauge II is a really nice accessory to monitor the HV battery pack temperature. I have a 4 kWh PHEV with the EV switch mod. I find that I'm often locked out of EV mode because the HV pack hits 114F. Also, the 2G (2007) Prius goes into fuel efficiency hell because of the heat down here in Miami. I've seen the SG report 131 on the HV battery pack. At that temperature, even the slighted cracking of the throttle under the lightest of load fires up the gas engine. This is the fuel efficiency hell mode. This is running the AC down at 75 on auto.

 

This is an interesting point. Consumers Reports did a longish test a few years ago as to whether it was more fuel efficient to run the A/C or open the windows. I don't remember the test conditions but it was a pretty hot day.

Guess what? The test vehicle got better fuel economy with the windows up and the A/C running. The better aerodynamics of having the windows up saved more fuel than the A/C "wasted."