[lagagnon]

Not sure how many are aware of the latest from Tesla's battery engineers:

https://electrek.co/2017/09/01/tesla-battery-expert-recommends-daily-battery-pack-charging/

The key paragraph in that article is this:
"One of those things is not charging to a full charge too often. Repeated full charges can negatively impact li-ion battery cells, which is why Tesla recommends to only daily charge to 90% capacity and to charge to 100% only when needed for long trips."

I suspect the battery charging management microcontrollers in the Volt are optimizing charging to ensure as long a life as possible for the battery pack, but I wonder if anyone here can point me to any published papers from the Volt engineers on how they are in fact optimizing the charging?

 

[obermd]

Which is why GM's engineers don't allow the Volt, and I assume the Bolt as well, to every fully charge the batteries.

 

[lagagnon]

obermd: that's is what I figured, but do you have any links to that information?

 

[flyingsherpa]

This is a state-of-charge (SoC) window thing. Say a battery's true capacity is 100kWh... the engineers will restrict it to only being charged in a window that is somewhat smaller than that, usually some off both the bottom and top end. For example, they might restrict the bottom 5kWh and top 5 kWh so the car is only able to use 90kWh... this is the SoC window. They do this because it drastically reduces cell degradation over many cycles. The smaller the window, the less degradation. GM was very conservative with the gen1 Volt and only allowed 65% SoC window (10.5 kWh on a 16kWh pack) to ensure it would last a long time. So when you think you are at 100% full, you're really only at around 85% full for what the battery can actual do (the 65% is roughly from 20 to 85% of actual capacity).

Pure BEVs want to have the most range possible, so they typically use a much large SoC window. I don't know exact numbers, but I believe Leafs and Teslas typically allow 90-95% SoC. Tesla offers "standard charge" and "range charge" to help limit issues.... the standard charge does what the article above says, it charges to a lower SoC for battery health reasons, since most daily trips don't need the full advertised range. Then when you go on a road trip, you do a range charge for max range. It's always been known that you should avoid range charging daily, I'm not sure why this article is "news".

So charge to full on the Volt all you want, it already has a large built-in buffer for longevity. But don't do range charging on a Tesla unless you need it.

 

[BAZINGA]

This really isn't news. It's been common knowledge for years. I suspect it's just a reminder aimed at all those NEW M3 owners that may not be so EV savvy.

 

[Steverino]

The Bolt has a "hilltop Reserve" seeting. When ON it limits max charge so those living at the top of a hill can pump up the battery with regen on the way down. The rest of us use it as an easy way to avoid 100% charges.

 

[llninja]

obermd: that's is what I figured, but do you have any links to that information?

Wikipedia has the answer

https://en.wikipedia.org/wiki/Chevrolet_Volt#Battery

Basically, the car has a certain sized battery, but only uses a percentage of that battery so 100% charging isn't possible. In other words 100% on the dash is something like 80% in reality. 0% on the dash is something like 25% in reality. These number change depending on which model year of Volt you are talking about

 

[viking79]

If you look at recent 400k mile Volt threads about Erick Belmer and his has like 142k EV miles, which is like 4000 charge cycles and still around 95% capacity. No need to worry. As others say, Volt is a range extended electric with a gas engine, they don't charge as high to protect the battery from voltage fluctuations when the generator is running.

 

[michaellax]

The Bolt has a "hilltop Reserve" seeting. When ON it limits max charge so those living at the top of a hill can pump up the battery with regen on the way down. The rest of us use it as an easy way to avoid 100% charges.

Yes, but you miss the point: If the Bolt EV's battery is really 65 KW and a 100% charge is only to 60 KW, you are wasting your full capacity with your hilltop reserve.

No one has pointed out to me any prescription by GM/Chevy in the Bolt EV manual to NOT charge to 100% like the Tesla report.

I paid for a 238 mile Bolt EV, not a "hilltop reserve" Bolt EV...

 

[jsmay311]

In respect to SOC windows, EREVs/PHEVs (like the Volt) cannot be fairly compared to BEVs (like Teslas or Bolt or Leaf).

Since EREVs regularly cycle through their entire usable battery capacity on a daily basis (and sometimes even more frequently) during typical use, they HAVE to have much more conservative SOC windows to avoid serious battery degradation.

BEVs, on the other hand, should literally never be drained all the way to "empty" and should only rarely be drained to very near "empty", and can therefore tolerate wider SOC windows.

Allowing the user to set the charge level to 80% or 90% most of the time and raise it to 100% seems like the best solution. That way you can "baby" the battery and maximize longevity most of the time, but also allow for max range when needed.

 

[llninja]

Yes, but you miss the point: If the Bolt EV's battery is really 65 KW and a 100% charge is only to 60 KW, you are wasting your full capacity with your hilltop reserve.

No one has pointed out to me any prescription by GM/Chevy in the Bolt EV manual to NOT charge to 100% like the Tesla report.

I paid for a 238 mile Bolt EV, not a "hilltop reserve" Bolt EV...

There's nothing in the owners manual, because there's nothing to worry about. I would avoid charging the Bolt using DCFC every day, but on level 1 or level 2, just plug it in and forget it. The car should be fine. Only time will tell.

If your commute is short, you might get into the habit of charging weekly instead of daily, and only filling the car to the max when you know you have a long trip ahead of you. Just don't get into a situation where your battery saving technique causes you to be forced to park and charge because you've exceeded your range.

 

[michaellax]

There's nothing in the owners manual, because there's nothing to worry about. I would avoid charging the Bolt using DCFC every day, but on level 1 or level 2, just plug it in and forget it. The car should be fine. Only time will tell.

If your commute is short, you might get into the habit of charging weekly instead of daily, and only filling the car to the max when you know you have a long trip ahead of you. Just don't get into a situation where your battery saving technique causes you to be forced to park and charge because you've exceeded your range.

On the other hand, my habit is to plug in every time. I don't want to think about it and the manual does not caution me otherwise!

If I need a full capacity charged drive, I paid for that ability! That is my habit.

I must assume that GM provided a "reserve" in the battery to cover for us to charge to 100% every night! Otherwise they would warn us accordingly.

 

[Upper5Percent]

On the other hand, my habit is to plug in every time. I don't want to think about it and the manual does not caution me otherwise!

If I need a full capacity charged drive, I paid for that ability! That is my habit.

I must assume that GM provided a "reserve" in the battery to cover for us to charge to 100% every night! Otherwise they would warn us accordingly.

Keep doing what you have been doing...GM has a much better Battery Management System than Tesla...

 

[Steverino]

I use Hilltop Reserve though I live in Flatland.

There is a reason GM limited charging on the Volt's battery: to preserve battery life. The Bolt's battery is not magic. It will degrade. Charging to 100% all the time is in general not a good idea if you want to minimize degradation, maximize longevity. I already get above the car's 235 miles range. Charging to 90% won't affect any travel I do. For those occasions when I have a 235 mile trip, I can turn off Hilltop Reserve. For the rest of the time, Hilltop Reserve baby's my battery automatically. Belt and suspenders.

 

[11715]

Keep doing what you have been doing...GM has a much better Battery Management System than Tesla...

Please fill us in on how GM system is better than Tesla. I don't recall reading anything on that topic so it would be interesting.

 

[Mister Dave]

EV owners want ultra-fast charging and technologies are available but these should be used sparingly as fast charging stresses the battery. If at all possible, do not exceed a charge rate of 1C. (See BU-402: What is C-rate?) Avoid full charges that take less than 90 minutes. Ultra-fast charging is ideal for EV drivers on the run and this is fine for occasional use. Some EVs keep a record of stressful battery events and this data could be used to nullify a warranty claim. (See BU-401a: Fast and Ultrafast Chargers)

Estimating SoC has always been a challenge, and the SoC accuracy of a battery is not at the same level as dispensing liquid fuel. EV engineers at an SAE meeting in Detroit were surprised to learn that the SoC on some new BMS were off by 15 percent. This is hidden to the user; spare capacity makes up for a shortfall.

EV makers must further account for capacity fade in a clever and non-alarming way to the motorist. This is solved by oversizing the battery and only showing the driving range. A new battery is typically charged to 80 percent and discharged to 30 percent. As the battery fades, the bandwidth may expand to keep the same driving range. Once the full capacity range is needed, the entire cycle is applied. This will cause stress to the aging battery and shorten the driving ranges visibly. Figure 4 illustrates three SoH ranges of an EV fuel

http://batteryuniversity.com/learn/article/electric_vehicle_ev

 

[Bluesideup]

Keep doing what you have been doing...GM has a much better Battery Management System than Tesla...

Please do tell us how much better GM battery management system is.

I mean we have seen Tesla's with 200,000 miles on them that get charged to 100% from superchargers just about everyday only lose 6%. So please go on and tell us this wonderful battery management system that GM has that could do better. Even though there is no GM car that can even charge as fast as the Tesla can yet I am still interested in how their management system is "much better".

https://techcrunch.com/2016/09/29/tales-from-a-tesla-model-s-at-200k-miles/

or around 7 percent loss at 250,000 miles:

http://insideevs.com/tesla-model-s-250000-miles/

Or is this just another bit of fake news?

 

[CYAOPEC]

Please do tell us how much better GM battery management system is.

I mean we have seen Tesla's with 200,000 miles on them that get charged to 100% from superchargers just about everyday only lose 6%. So please go on and tell us this wonderful battery management system that GM has that could do better. Even though there is no GM car that can even charge as fast as the Tesla can yet I am still interested in how their management system is "much better".

https://techcrunch.com/2016/09/29/tales-from-a-tesla-model-s-at-200k-miles/

or around 7 percent loss at 250,000 miles:

http://insideevs.com/tesla-model-s-250000-miles/

Or is this just another bit of fake news?

I"m guessing the prior poster may have been referring to GM's battery laboratory. Tesla reminds me a bit of Pentax--they make great cameras with some innovative features. But can you really freeze a Pentax DSLR in a block of ice then thaw it out, pour lighter fluid over it, set it on fire, then cool it off and find it's still working like a Nikon D series camera? The Volt with 400k miles shows GM's validation procedures are spot on. I personally would have no reluctance buying a Tesla. But I don't know if they actually test their packs in the same way GM does. But then maybe they do . . . I'd love to see their pack testing laboratory, that is if they even have one.

 

[JerryInSanDiego]

I drove my 2011 Volt for 5 years, charging it fully every day. When I traded it for a 2016 Volt it still had exactly the full range that it did when I bought it. I'm doing the same on the 2016.

 

[llninja]

I"m guessing the prior poster may have been referring to GM's battery laboratory. Tesla reminds me a bit of Pentax--they make great cameras with some innovative features. But can you really freeze a Pentax DSLR in a block of ice then thaw it out, pour lighter fluid over it, set it on fire, then cool it off and find it's still working like a Nikon D series camera? The Volt with 400k miles shows GM's validation procedures are spot on. I personally would have no reluctance buying a Tesla. But I don't know if they actually test their packs in the same way GM does. But then maybe they do . . . I'd love to see their pack testing laboratory, that is if they even have one.

My fear of Tesla is a bit different. As long as they are in business, I believe Elon will try to do the right thing. Their 8 year unlimited mile battery warranty is good enough for me. I worry that with the release of the Model 3 and the freight train "manufacturing hell" they are about to face while they are bleeding cash, people will slow Model S and X purchases, and there will be this big chasm between scaling up and profitability of the Model 3. If the Model 3 stumbles like the Chrysler Pacifica Plug-in, there may not be a company left to honor that warranty. Would the feds jump in to bail out Tesla like they did with GM? Who knows.

I'm hope Tesla pulls this off, but I also cancelled my Model 3 reservation.