Tonneau cover- better to leave covering the cargo area?

IMO, you will benefit more by doing what you are doing now. Everything I have read so far seems to point to heat being the enemy of the traction battery. And we both know how hot it gets down here. Take advantage of every bit of shade you can, and enjoy your Prius.

 

Not sure about the long term wear leaving the cover extended. I have a Sun Shade front and rear. See pictures:

 

I have the same thing that HGS has, but it is for the front wind shield. I definitely recommend these type of shades for the Prius.

 

I also use Weather Tech Deflectors and keep windows down 1 inch. I monitor my temperatures and using shades and deflectors really helps keep the battery cooler. The second picture is during a very hot day when I made a couple of trips and let the battery heat soak. Normally my battery is about 35 to 40 C when leaving work at 3:30 PM rather than closer to 45 to 50 C before the shades and deflector with windows cracked 1 inch.



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The rear shade should not wear out, it's intended to be used as a cover. I've never read anybody actually wearing one out yet.

 

The suction cups work well if wetted first. Saliva works.

With the dark deflectors, you can't see that the windows are down a bit. If someone yanked off the deflectors they could put something in there to try and unlock the door. I don't have a problem at my gated work parking lot.

There is no difference in gas mileage.

From what I learned by observation and reading on PC, if I drive on very hot days and then leave the car for a few hours (go out for lunch then drive home 3 hours later) AND park with a very high battery charge (70 - 80 %), the battery will heat soak and be above 50 C for the drive home. I now will let the battery drain down to 60% before leaving it (sit with AC on LOW/ max. Fan, headlights on). It only takes about 5 or 6 minutes to drain it down.

The car will protect the battery when the battery temperature is above 125 F (50 C). The engine runs all the time and the battery is not used much until it cools down. In 15 minutes I've seen the battery cool from 125 F to 112 F (50 C to 44 C) using AC LOW/max. Fan).

It's best not to let the battery get above 125 F (50 C) if possible. I think doing this day after day can shorten the life of the battery.

With my routine, even on hot days my battery temp. stays low.

 

The standard roll-up cover would probably eventually sucuumb to UV if left in place, if the rear glass is not heavily tinted, and if the car is parked tail to the sun for several summers. Haven't heard of that actually happening to anyone yet, though. How much difference does the cover make to battery temperature?

I mostly park with the car facing west-southwest, so the sun comes mainly from the left side and front during the sunniest parts of the day, so I don't need to be as concerned about rear solar heating. I might spring for a better front shade for next summer.

 

I kick myself to this very day for leaving behind a perfectly good tonneau cover when I traded in my 2008. The car had just over 190K on it and might have gotten resold or auctioned. There wasn't anything obviously wrong with the car, well, I was just starting to hear a wheel bearing maybe. And the clock spring in the steering wheel was failing. I should have grabbed the cover when I was swapping stuff over to the "new to me" 2011 in the parking lot. Excitement, just didn't notice till later. Oh well. Find one on eBay maybe.

 

While in Florida back in 2011 I had the windows tinted a bit. The heat coming in was incredible. That helped. Window shades do the rest when we have to park in the sunshine and heat. I have used the window deflectors on other vehicles and they work very well. Never had a break in issue with them on and the windows down a bit.

I don't have window deflectors on the Prius. Our IV has that solar roof and the fan that pumps in air when temps are more than 80 degrees in the cabin. Bad thing is... in Florida, the outside air temperature can be 97F and with incredible humidity, so not too much that it can do for comfort when you get into the car. If I didn't have that solar fan option, I would probably have the window deflectors installed.

 

B.Roberts,

I see you're from Maine.

I lived in Caribou, Maine (Loring AFB) for four years back in the early 80's. What a wonderful place for that time in my life. Also lived in Massachusetts for seven years. New England has so much history and character. There's not much need for air conditioning except a few days in the summer. In Mass. we didn't have central air, just a small window air in our bedroom.

I wonder what the effect of freezing temperatures is on the Traction Battery. Is freezing the TB just as bad as cooking it in the hot states? I'm guessing probably not, but I've had aircraft batteries freeze in the Dakota's when it's -20 F.

 

I've lived in all 4 corners of the States and must say they all have something unique to offer. If you live away from the coast of Maine, say 5 or more miles inland you will probably need air conditioning for about 2-3 months during summer now. Not continuously, but we use it more and more now. First half of our Summer this years was perfect... highs in the 70s and lows in the 50s.

When we returned from a stay in Florida that lasted from early May to about mid July, the Maine Summer temperatures started to move up, along with the humidity. Highs bumped up into the mid and upper 80s with dewpoints that were in the upper 60s. That for us is hot and humid. Nighttime lows were only falling to the lower 70s, so the A/C was started up and ran through much of August and part of September. And temperatures and humidity are coming back up right now. We may have to fire it up at night to sleep comfortably the next couple or 3 days from what the forecast numbers are trending.

Traction battery seems to do OK in the cold. Since we've had Prius, first one bought in 2005 and this one in 2011, about the coldest temperature we have seen here is a couple of nights near 10 below zero F. In our first few Winters in Maine from 1995 to about 1998 we had a couple of 20 to 22 below zero events. None that cold since. We live on a small ridge that's about 15 miles inland and a little over 700 feet above sea level, so we don't get the low drainage cold temperatures that settle in some of those locations.

Don't think I've ever heard of a traction battery freezing or misbehaving in the cold. Maybe one of our Canadian members can enlighten us about cold traction battery performance, or lack there of when it gets really cold.