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Adventures in Battery Conditioning (relim. findings IRT battery cooling criteria)

19132 Views 78 Replies 24 Participants Last post by  bro1999
So I've been gathering data and observing when and how my car has been running it's battery cooling processes under different scenarios. I've gathered quite a bit of preliminary data, I haven't poured over the Torque logs yet (I'm not a data analysis guy) so there are some gaps but I feel like I have enough of an insight into when and how the car does battery conditioning to be of use to fellow owners (especially since we're still knee deep in summer.

The first thing I've observed is that the car REALLY cares about whether it's "plugged in" and will definitely cool sooner and to a lower temperature if it's plugged in vs not. FTR I've only observed being "plugged in" to a L2 charger, I don't know whether connecting to L1 or DCFC will produce the same results.

The second major criteria is whether or not the car is "on", this changes the conditioning behavior both "plugged in" and "unplugged".

I have yet to observe any evidence of battery conditioning when the car is both "off" and "unplugged". I've seen battery temps as high as 37C/99F with ambient temps as high as 42C/108F and the car has not decided to cool the battery even with high states of charge (above 80%). I have heard that other owners have witnessed off/unplugged battery conditioning but I've never seen it so I have no idea what temp might be required to trigger it other than above 37C.

One of the things I don't know is what specific temperature sensor(s) the car is looking at when it decides to cool the battery. There are several OBDII PIDs for battery temperature and several for electronics temperature. Most of the time these sensors all have different temperature measurements within 1C-3C of each other. I'm sure this is something that could be nailed down looking at the data.

Also note that all the numbers I'm using are Celsius meaurements as observed via Torque because that's what the car uses. I've converted many of these numbers to Farenheight for the benefit of my fellow countrymen but I've used standard rounding so 31C becomes 88F not 87.8F.

There are two main modes of battery cooling that I've observed, I'll call these "aggressive" and "weak" modes. I have only observed aggressive mode cooling when the car was plugged in.

Under aggressive mode cooling the car will start cooling at about 33C/91F and stop cooling at about 27C/81F (battery temperature)

Under weak mode cooling the car will start cooling at about 35C/95F and stop cooling at about 31C/88F.

OK with all that out of the way here is the list of different scenarios I have seen.
off/unplugged - n/a
on/unplugged - weak mode
off/plugged/charging - none
off/plugged/not charging (charge complete or charge not needed) - aggressive mode
on/plugged/charging - aggressive mode

Some other notes:

If the vent fan for the passenger compartment is on when the car is performing battery cooling you will get cool air into the cabin whether or not you have "heat and AC" on in the climate settings. Interestingly this will also cause the displayed percentage of your power used for climate settings to increase and the car will attribute more power to climate settings than it will to battery conditioning by about a 2:1 margin.

The converse is not true, if you are running cabin air conditioning and the battery is as warm as 32C/90F the car will make no effort to cool the battery.

If anybody wants to pour over the data themselves I've got all my Torque logs uploaded to a shared Dropbox folder. Feel free to peruse.

I'm actually quite disappointed in the decisions that GM made when designing the battery conditioning profiles for the Bolt. Really the only time the car decides to prioritize cooling the battery is when the car is plugged in. I'd expect that most people who live in hot climates are like me and do not usually have ready access to an L2 charger during the hottest part of the day. Now I understand that many people would not want to see their range being decreased due to battery conditioning but IMO they have gone too far and are allowing the battery to get and stay much too hot which will negatively effect the long term capacity retention of the battery.

Between this frankly pathetic approach to battery conditioning and the lack of options for limiting the maximum SoC it's abundantly clear to me that GM does not remotely prioritize the long-term health of the battery. I expect that a Bolt battery will still significantly outlast a Leaf battery that completely lacks active battery cooling but I don't expect it to perform nearly as well over the long term than a Tesla Model S battery. Being that the average amount of time that new car buyers keep their cars is only about 6 years combined with the reality that many Bolt drivers are lessees instead of purchasers I suspect that GM (correctly) figures that most of the people who will have to deal with the repercussions of this approach will be 2nd or 3rd owners.
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Love how data driven you are.

It's unclear to me that GM has not prioritized battery longevity enough, as there are way too many variables at play. Perhaps the Bolt is more temperature tolerant than Tesla. Perhaps the max and minimum voltages are more conservative than Tesla.

Time will tell, but I'm sure the Bolt batteries will hold up better than the Leaf. I've heard of people complaining about battery degradation in their Gen I Leaf that is only 3 years old.
It could be that not being as aggressive about battery conditioning when on battery power alone is the better way to preserve battery life. While temperature is a component of battery longevity, so is battery use. The less use it gets, the healthier it is. There is some balance to be had between maintaining a healthy temperature range, and not excessively using the battery. Given that, it makes complete sense to maintain tighter temperature control when wall power is available, and be a little more loose when it is not.
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So I guess this means that it is better to plug in the car when not in use during the day.
I would say generally yes, especially if Hilltop Reserve setting is used. Then there is the added benefit of the car checking the 12v battery more frequently, I believe.

I don't see much benefit in going multiple days without plugging in, especially when hilltop can be used to limit the charge. It just makes it more difficult to remember plugging in when needed since you get out of the habit of always plugging in.

My wife used to plug in the Prius anytime we went somewhere together, which was all the time. On the few occasions she wasn't with me, I'd forget to plug in.
There was that Canadian guy with the hockey avatar who ran his battery SoC very low and tried to DCFC in very cold temps. It refused to charge saying he had to connect to L2 first.

I'm guessing there is some state of charge, perhaps around 40%, that prevents even the weak conditioning when the car is off.

My WAG is there is "aggressive" conditioning when plugged in, "weak" conditioning when unplugged and on, and "even weaker" conditioning when unplugged and off when the SoC is above some threshold, and no conditioning below that.

Hasn't this been thoroughly discussed in the cold discussion? I would think similar behavior exists with hot temperatures.
As Vertiformed pointed out, I don't think this is a fair statement:

"Between this frankly pathetic approach to battery conditioning and the lack of options for limiting the maximum SoC it's abundantly clear to me that GM does not remotely prioritize the long-term health of the battery."

GM had to weigh the cost of giving the owner more control of limiting charging vs the cost of doing so, which includes the cost of dealing with people that accidentally set things and get frustrated not knowing what they have done, or those people who use the feature and then drive to a low state of charge, which itself creates wear on the battery.

Nobody has addressed the point I brought up that the simple act of using the battery creates wear, and that likely explains why there is a "weak" battery conditioning that occurs when the car is not plugged in. It's not that the engineers were lazy about thermal management, but that there is a trade-off to everything, and all things considered, a "weak" thermal management when unplugged is the right behavior for most people.

All that said, I appreciate the shared experiment, and the effort to understand how best to preserve the health of the battery. While I disagree with the conclusions raitchison has come to, I appreciate the data and the discussion.
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