Vertiformed
Posts: 4
Joined: Sat Aug 18, 2018 8:52 pm

What is meant by a “long period”

Sat Aug 18, 2018 9:00 pm

Here's a question for the Chevy folks, in the manual for the car, it says:

Do not allow the vehicle to remain in temperature extremes for long periods without being driven or plugged in. It is recommended that the vehicle be plugged in when temperatures are below 0 °C (32 °F) and above 32 °C (90 °F) to maximize high voltage battery life.


One key question is just how long a “long period” is. Is a “long period” a few hours while at work, or is it a few days while away on vacation?

Also, this same advice is printed verbatim in the Spark EV manual, but the Bolt has been touted as having a battery with better thermal performance. Are there operational differences (either what the car does or what owners should do) between the two?

I realize that the whole question is of how best to take care of the battery and what the Bolt's TMS does isn't something the Chevy reps like to wade into (even though it would be super helpful to get clarity on all these issues), but here the question is much more direct, what does the text in the car's manual actually mean. I hope a Chevy person can give a clear answer at least to this part.

SeanNelson
Posts: 1462
Joined: Tue Jul 05, 2016 2:43 am
Location: Vancouver, BC

Re: What is meant by a “long period”

Sun Aug 19, 2018 2:11 am

Vertiformed wrote:One key question is just how long a “long period” is. Is a “long period” a few hours while at work, or is it a few days while away on vacation?

These kinds of things are not binary - it's not a "long period" if it's greater than xx hours but everything is just fine if it's less than that. What the manual is essentially saying is that the longer you leave the battery to cook or freeze, the bigger an impact it will have on battery longevity. And one exposure to those conditions won't be as bad as if you make a regular habit of it.

Generally speaking, the battery has a lot of mass and is relatively slow to heat or cool when the car is just left to sit there. But it will reach ambient temperature eventually, I'd probably give it around 12 hours to do so. The more extreme the outside temperature, the faster the battery's temperature will move outside the preferred range.

So as temperatures become more extreme and the exposure to them lengthens, the more important it is to leave the car plugged in so that it can use its thermal management. As a general rule, I'd posit that plugging it in is pretty important if you leaving the car alone for a day or more when weather that could turn extreme. I wouldn't worry quite so much for 8 hours at work, although specific conditions such as parking on really hot asphalt before walking away for several hours might influence that.

Vertiformed
Posts: 4
Joined: Sat Aug 18, 2018 8:52 pm

Re: What is meant by a “long period”

Sun Aug 19, 2018 3:01 am

SeanNelson wrote:What the manual is essentially saying is that the longer you leave the battery to cook or freeze, the bigger an impact it will have on battery longevity. And one exposure to those conditions won't be as bad as if you make a regular habit of it.


I understand why you and others might interpret it that way.

Generally speaking, the battery has a lot of mass and is relatively slow to heat or cool when the car is just left to sit there. But it will reach ambient temperature eventually, I'd probably give it around 12 hours to do so. The more extreme the outside temperature, the faster the battery's temperature will move outside the preferred range.

So as temperatures become more extreme and the exposure to them lengthens, the more important it is to leave the car plugged in so that it can use its thermal management.


The car is capable of performing battery conditioning while parked and not plugged in (although various people on Bolt forums debate the extent to which this happens—it certainly happens less than when plugged in or powered on). Thus there is no reason why the car needs to suffer any thermal-stress-related degradation at all when parked not plugged in.

As a general rule, I'd posit that plugging it in is pretty important if you leaving the car alone for a day or more when weather that could turn extreme. I wouldn't worry quite so much for 8 hours at work, although specific conditions such as parking on really hot asphalt before walking away for several hours might influence that.


I lean towards thinking along similar lines, but a clarification from someone from GM might help us have a better idea.

SeanNelson
Posts: 1462
Joined: Tue Jul 05, 2016 2:43 am
Location: Vancouver, BC

Re: What is meant by a “long period”

Sun Aug 19, 2018 3:06 pm

Vertiformed wrote:The car is capable of performing battery conditioning while parked and not plugged in (although various people on Bolt forums debate the extent to which this happens—it certainly happens less than when plugged in or powered on). Thus there is no reason why the car needs to suffer any thermal-stress-related degradation at all when parked not plugged in.

Yes, but it will only do that if it's got enough juice left in the battery. So "long period" needs to take that into account - if you're parking the car with the battery pack partially run down then "long period" is anything that might cause thermal management to use up more power than you need or cause the car to cease thermal management before you get back to the car.

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