Battery Management

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like2bike

Well-known member
Joined
Oct 17, 2016
Messages
67
Location
Long Island, NY
Has anyone reverse-engineered any of the Bolt's battery management features? Cell balancing, temperature conditioning, etc. As I've stated before, I think the owners manual avoids informing owners of the battery details, even more so than Nissan.
 
Would be nice if someone developed "BoltSpy"

So, what are the best practices for this large a battery?
How low to let it get before recharging if you only average about 30 miles a day?
How often to charge to 100% for balancing?

I'm used to a 24 kWh pack, but with 60 kWh, for every day use, I might not need to charge more than once a week if I let it run low.
 
DNAinaGoodWay said:
Would be nice if someone developed "BoltSpy"

So, what are the best practices for this large a battery?
How low to let it get before recharging if you only average about 30 miles a day?
How often to charge to 100% for balancing?

I'm used to a 24 kWh pack, but with 60 kWh, for every day use, I might not need to charge more than once a week if I let it run low.

There are two schools of thought, but all agree...avoid high levels of charge. One school of thought is to keep the battery in the mid range. The "Dahn" school of thought, which I agree with, is to keep the battery toward the low end.

In any event, DO NOT fully charge, run down over a week to a low level, and then fully recharge.

In my case, I plan to avoid going over 60%-70% SOC in every day use, and to recharge back to the level daily. I expect to use about 40% per day, so I'll rarely go below the 20%-30% area but still have a comfortable reserve.

Furthermore, I will use the features to charge up to 40% immediately upon plug-in, and then do the remainder of the charging just-in-time for my morning departure.

You should never need to charge to 100% just to accomplish balancing. I'm certain the battery will balance just as well with the hilltop setting invoked. I would consider the hilltop setting as normal, full charge as a special case to be avoided except as necessary.
 
michael said:
DNAinaGoodWay said:
Would be nice if someone developed "BoltSpy"

In any event, DO NOT fully charge, run down over a week to a low level, and then fully recharge.
Could you clarify how much of this sentence is controlled by the phrase: DO NOT... thank you.
 
He means, I think, that sitting at near 100% (indicated) for a few days, then getting a full charge the next week and again sitting around near full, is to be avoided when possible. If you charge to 100%, then try to use the car ASAP, even if it only lowers it 10%.
 
I think he means the whole sentence. Deep cycling bad.

I like the hilltop mode. Nice feature. Especially since I live atop a hill.

Without a "spy" app, how can we know how balanced the cells are? There's probably balancing at low SOCs, but would maybe a monthly full charge, driving soon after, be beneficial?

I average 10 kWh/day or less, usually charging every other day, and my Leaf's pack has done well. But I'm in MA, so the climate is right. If I let a Bolt run down to 30-40%, I'd still have about the range I have with a full Leaf.
 
It seems like setting Hilltop mode is probably a no brainer, provided you don't need the full range. At worst it reduces your range by a small amount, but it can't hurt anything.

Nissan Leafs seem to have significant issues with battery degradation, even the newer models. Hopefully the Bolt will fare better since it actually has active temperature management on the battery. But really it's all just speculation right now. We'll need to see in a few years how the battery has held up, and what specific techniques work best.

While it seems like suggestions are to not run down to low levels, I wonder if setting hilltop as your max, and then running down to say 50% before recharging would be reasonable? That would keep the discharge cycle between 50-90%. On the other hand you could also run between 20-60%.
 
First - I have been running my car from about 90% down to about 25% before charging. This is mostly due to convenience since my last car had to be charged daily and now I can go four days. Oh, the freedom.

I thought about the design that went into this car when choosing on a routine for myself; should you charge to full? Probably not. How can I tell? The engineers thought it prudent to give us a mode that only charges to 90%. Should you only charge to 60%? Probably not. How do I know? The engineers did not allow for a simple way to do this in a car that is otherwise driven by efficiency. If it were known how to manage a battery for the life of it while maximizing utility, then I would like to think they would have written a blurb in the manual. Since all we got was to not let it sit at fully charged, I am willing to bet there is a lot of speculation going on with these recommended methods for managing the batteries.

Want a real answer? Ask an engineer. Until then, take it all with a grain of salt.
 
I am an electrical engineer and I work in a closely related industry.

To clarify....if you need charge only once a week DO NOT fully charge and then run down to zero and repeat weekly. Keep it in a narrow range, toward the middle or toward the lower end, depending on who you believe.

I personally believe Professor Jeffrey Dahn, who is an electrochemist who studies lithium batteries and a consultant to Tesla. He recommends keeping toward the lower end. Most people seem to believe otherwise, feeling that there is something harmful about a low SOC. I believe Dahn, but also believe the difference is small. What is harmful is high SOC and high temperature; and particularly both at the same time.

Tesla DOES provide the option to charge to pretty much any desired level. That GM does not should not be construed as meaning this would be without benefit. GM has disguised the "normal charge" and "extended charge" as hilltop and normal to get around stupid EPA rules which reduced the rated range if this option is provided.

Early Leafs, for example, provided 80% and 100% charge settings, and the EPA rated their range based on the average (90%). By eliminating the 80% option, Nissan got an increase in rated range without changing anything about the actual drive system.

And come to think about it, GM offers the 40% charge option. One could argue they think that a really great SOC.
 
Nagorak said:
It seems like setting Hilltop mode is probably a no brainer, provided you don't need the full range. At worst it reduces your range by a small amount, but it can't hurt anything.

Nissan Leafs seem to have significant issues with battery degradation, even the newer models. Hopefully the Bolt will fare better since it actually has active temperature management on the battery. But really it's all just speculation right now. We'll need to see in a few years how the battery has held up, and what specific techniques work best.

While it seems like suggestions are to not run down to low levels, I wonder if setting hilltop as your max, and then running down to say 50% before recharging would be reasonable? That would keep the discharge cycle between 50-90%. On the other hand you could also run between 20-60%.

From the standpoint of battery life, I would much rather run between 20-60 rather than 50-90. On the other hand, it depends on how much or little reserve makes you comfortable.

Your car is a $20,000 battery on wheels. You don't want to wait a few years to see how they are holding up. You should use the best possible practice from the beginning.

I agree, hilltop as a normal practice. I would try to stop charging before it reaches 90% as often as practical.
 
I don't think I'll have any problems keeping it in a middle SOC most of the time. Probably twice a week will do it.

Here's a concern though: it does get cold here, and this page of the manual implies if I don't keep it plugged in at my workplace parking lot, it may not start in winter. Really? What if I can't plug in? It doesn't mention an ambient temperature range.

IMG_6383.JPG
 
michael said:
From the standpoint of battery life, I would much rather run between 20-60 rather than 50-90. On the other hand, it depends on how much or little reserve makes you comfortable.

Your car is a $20,000 battery on wheels. You don't want to wait a few years to see how they are holding up. You should use the best possible practice from the beginning.

I agree, hilltop as a normal practice. I would try to stop charging before it reaches 90% as often as practical.

I guess the trade-off ultimately is with convenience. We could charge to only 40% even, but then the car has effectively become a short range EV. That could work, I suppose, provided you didn't have to drive long distance on short notice.

In any case, in general you'd say there's less risk of low levels of SOC? So going below 20% sometimes would be better than being at 90% regularly?
 
^Good point, good to have a reserve for unexpected driving needs.

These are the only other references I can find in the manual on cold weather:

IMG_6387.JPG

IMG_6386.JPG

While it recommends keeping it plugged in below freezing, the danger is leaving it in extreme cold for days. IIRR, that was below -10F for the Leaf, so probably similar here. Not a problem for one work day.
 
I think he means the whole sentence. Deep cycling bad.

Deep cycling isn't generally "bad" for lithium packs. It will kill NiMH packs and shorten the life of SLA packs a lot, but lithium cells tolerate deep discharges well, provided the pack isn't left at a SOC in the single digits for long. Leaf drivers have noted no correlation between using most of the pack's capacity and pack life. It's letting them sit at a high SOC for long periods, leaving them hot, and charging while hot, that shortens life and decreases capacity. So if you need to go from 95% to 10% often, go ahead. Just recharge as soon as you are done driving if it's at 10%, and try to avoid leaving it at 100% indicated (~90% actual).
 
Personally I'm going to follow GM's recommendations in the manual. Presumambly they know what's best for the pack since they're the ones on the hook for replacing the pack if something goes wrong in the first 8-years/100K miles of it's life. That basically means plugging it in every night to charge regardless of how much I've driven it that day. It also means using hilltop reserve because I live on a hill and want to have some headroom in the pack for regen braking. If I plan to not drive the car for over a month, then I'll park it unplugged with only 15% remaining. Otherwise I'll leave it plugged in so the car can do it's battery management thing if the temp falls below 32F or gets above 92F (both of which are extremely rare events living on the coast near SF).
 
I'd want to look at the ambient and pack temps. (Does the Bolt even have a battery temp gauge?) If the weather were mild, I'd be more concerned with keeping the pack well below 100% indicated SOC than about enabling the TMS. If it were very hot or very cold outside, then I'd plug in - unless the pack wasn't hot in hot temps. Remember that GM is trying to suggest that everyone do what will cause GM the least problems overall, not what will make the individual packs last best past the warranty period.
 
LeftieBiker said:
I think he means the whole sentence. Deep cycling bad.

Deep cycling isn't generally "bad" for lithium packs. It will kill NiMH packs and shorten the life of SLA packs a lot, but lithium cells tolerate deep discharges well, provided the pack isn't left at a SOC in the single digits for long. Leaf drivers have noted no correlation between using most of the pack's capacity and pack life. It's letting them sit at a high SOC for long periods, leaving them hot, and charging while hot, that shortens life and decreases capacity. So if you need to go from 95% to 10% often, go ahead. Just recharge as soon as you are done driving if it's at 10%, and try to avoid leaving it at 100% indicated (~90% actual).

That has been my experience with the Leaf. I've deep cycled it many times in the way you describe with no adverse effects.

Since the Bolt has thermal management, it shouldn't have the same problems with heat that Leaf has. Just some loss of charge to the TMS. Which is why the manual wants us to plug it in all the time.
 
LeftieBiker said:
I'd want to look at the ambient and pack temps. (Does the Bolt even have a battery temp gauge?) If the weather were mild, I'd be more concerned with keeping the pack well below 100% indicated SOC than about enabling the TMS. If it were very hot or very cold outside, then I'd plug in - unless the pack wasn't hot in hot temps. Remember that GM is trying to suggest that everyone do what will cause GM the least problems overall, not what will make the individual packs last best past the warranty period.

With a Bluetooth OBDII reader and the Torque app on Android (or EngineLink on iOS) you can get access to the pack temperature sensors, and pack SOC, and a variety of other readings. People are using the Volt PIDs as a starting point to get more info on the internals of the Bolt.
 
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