Hilltop Reserve

[michael]

What is the possible upside of pushing the battery every night? I sure wouldn't do that

 

[oilerlord]

I am going with the former theory and charging my Bolt EV every night without Hilltop Reserve.

My instincts just tell me that GM would tell us in the manual to use Hilltop Reserve for this purpose, or give it another name, if indeed it purpose was to give the battery more useful life!

Certainly GM Financial as the ultimate owner of all of the leased Bolt EV's to date would want the leasees to know this information and promote this activity for the residual value of all of their Bolt EVs coming back to them!

Yet, not a peep out of GM!

In marketing the Bolt, GM cared about two main objectives:

1.) The car had a EPA range of 200+ miles.
2.) They could sell it for $30,000 (after incentives).

These were (and are) the predominant "game changer" media talking points about the car. Mission accomplished.

It stands to reason that in accomplishing both objectives, no less and no more than 60 kWh of battery was required to achieve those 238 miles - AND being able to hit that $30K price point.

As the "ultimate owner" of all leased Bolts being returned; you'd think GM would care about the longevity of the battery - but really; they don't. Think about it: In the big picture, they are only going to sell 20,000 - 25,000 Bolts per year (or perhaps less when Tesla Model 3 production ramps up). In 2016, GM sold 10 MILLION cars & trucks worldwide. The Bolt's 0.25% contribution to overall sales isn't much more than a rounding error. With that in mind, do you really think GM cares about the minutia of how many people use hilltop reserve?

http://money.cnn.com/2017/02/07/news/companies/gm-record-sales-profits/index.html

I'd agree with Michael, I think without hilltop reserve - GM is using most of the total battery capacity. If GM really did care about long term battery longevity, they would have engineered a buffer of at least 15% into it, and capped usable capacity somewhere between 50-55 kWh. Instead, they made it a user-selectable setting named "Hilltop Reserve". Putting that decision into the hands of the owner isn't necessarily a bad thing as we get to make the choice between range when we need it & battery health for the long term. I think GM should have instead called it "Battery Saver" - which really, is what people who intend to drive the car for the long term want to do.

 

[michael]

I agree. They wanted to wring out every EPA mile they could out of the car, and doing that requires pushing the battery hard. The battery fade warranty allows pretty substantial declines in capacity before warranty replacement is required.

And frankly, that's reasonable. Suppose they had derated the battery by 10%...how would one feel if he ran out of juice 20 miles from his destination. Wouldn't we say "They should have unlocked the full battery capacity and let us make use of a limited portion except when necessary..." Well, they did that.

 

[oilerlord]

I agree. They wanted to wring out every EPA mile they could out of the car, and doing that requires pushing the battery hard. The battery fade warranty allows pretty substantial declines in capacity before warranty replacement is required.

And frankly, that's reasonable. Suppose they had derated the battery by 10%...how would one feel if he ran out of juice 20 miles from his destination. Wouldn't we say "They should have unlocked the full battery capacity and let us make use of a limited portion except when necessary..." Well, they did that.

Absolutely reasonable.

Conversely, Mercedes / Tesla did the exact opposite with my car. My total battery capacity is 36 kWh, but it's capped at 28 kWh usable. They offer a "Range Plus" option that unlocks 5.6 kWh - allowing the driver to use 33.6 kWh out of the 36 kWh. It's recommended only to use this feature occasionally as doing it on a long term basis is detrimental to the long term health of the battery. The operator's manual warns:

"Using RANGE PLUS shortens the service life of the battery. Therefore, only use RANGE PLUS if, for example:
- long journeys are planned or
- the availability of charging stations at the destination is limited"

Clearly, Mercedes / Tesla recognizes that using most of the total battery capacity, most of the time, isn't a good thing with my car. I'd suggest the same is true with all EV's.

 

[LeftieBiker]

I agree. They wanted to wring out every EPA mile they could out of the car, and doing that requires pushing the battery hard. The battery fade warranty allows pretty substantial declines in capacity before warranty replacement is required.

And frankly, that's reasonable. Suppose they had derated the battery by 10%...how would one feel if he ran out of juice 20 miles from his destination. Wouldn't we say "They should have unlocked the full battery capacity and let us make use of a limited portion except when necessary..." Well, they did that.

The obvious solution that is yet to be implemented is to have an Emergency Reserve that has to be manually activated by the driver, like the Reserve position on motorcycle petcocks. This would allow for emergency use of most of the reserved capacity, without the extra stress on the pack from constant use of the last few KWHs.

 

[SeanNelson]

The obvious solution that is yet to be implemented is to have an Emergency Reserve that has to be manually activated by the driver, like the Reserve position on motorcycle petcocks. This would allow for emergency use of most of the reserved capacity, without the extra stress on the pack from constant use of the last few KWHs.

You're assuming that for the battery's health that reserve has to be at the bottom end of the charge range. If the reserve is at the top end of the range then it has to be selected when you charge the vehicle, not when you run out of charge. I don't think there's any reasonable way to define an additional charge as an "emergency" since it's something that pretty much by definition you're planning for.

 

[michaellax]

Well until GM actually makes a statement about the issue, we are debating about how many angels can dance on the head of a pin!

And none of the three of you (not referring to Sean, who posted in the middle of my drafting) have any skin in the game; and I only have a limited amount; so although you are entitled to your opinion, it is of limited value because, so far, none of the three of you have put your money where your mouth is vis-a-vis purchasing a Chevy Bolt EV!

And listening to this advice actually hurt me this weekend, as I started to not plug my Bolt EV in every night and decided at the last minute to take a drive to Moreno Valley Sunday and back, without a full charge!

And although I had a Mileage Gauge indication of 89 miles remaining to come home and probably could have made it "on electrons" I used the EVGo in Moreno Valley for 30 minutes just to be safe; a needless delay had I had my full charge when I began!

 

[LeftieBiker]

The obvious solution that is yet to be implemented is to have an Emergency Reserve that has to be manually activated by the driver, like the Reserve position on motorcycle petcocks. This would allow for emergency use of most of the reserved capacity, without the extra stress on the pack from constant use of the last few KWHs.

You're assuming that for the battery's health that reserve has to be at the bottom end of the charge range. If the reserve is at the top end of the range then it has to be selected when you charge the vehicle, not when you run out of charge. I don't think there's any reasonable way to define an additional charge as an "emergency" since it's something that pretty much by definition you're planning for.

I'm assuming that there is some reserve on the bottom end that should be available if only used occasionally. I should have been more clear about that. It would also be a good idea to have a "charge to 98%" as well, with the extra charge being bled off by the climate control if not used within a few hours.

 

[michaellax]

What is the possible upside of pushing the battery every night? I sure wouldn't do that

To obtain the maximum range when I need it unexpectedly. Exactly what happened to me last Sunday.

Don't you own a Volt, so by definition you can't push the battery every night anyway!

 

[oilerlord]

What is the possible upside of pushing the battery every night? I sure wouldn't do that

To obtain the maximum range when I need it unexpectedly. Exactly what happened to me last Sunday.

Michael is suggesting what's best for the long term health of the battery based on his own experience and scientific research he's gathered and posted in other threads. You're certainly free to fully discharge / fully charge / and leave your car plugged in all the time to obtain the maximum range when you need it. Most people do exactly that however studies have shown that practice has long term detrimental effects on the battery.

Lithium ion battery packs, and their characteristics aren't all that different between a Bolt, Volt, Leaf, or my B250e. Some may have better chemistry & thermal management than others but ultimately, they all degrade. They all have an optimum state of charge and depth of discharge that, when adhered to over time, extends their lifespan.

You may have been caught without enough range in your battery, but the science behind what extends or reduces a lithium ion battery pack's life is sound. That same research shows that a battery pack with a larger percentage buffer will last longer than a battery with a smaller percentage buffer. It's one of the biggest reasons people are still driving their Gen 1 Volts for 200,000 miles and report very little battery degradation. Some of those battery packs used only 10.3 kWh out of their 16 kWh capacity. If that same engineering was applied to the Bolt, your car would use only about 2/3 of it's total capacity. You'd have a maximum range of only ~180 miles, but your battery would last a long, long time. Some choose to use Hilltop Reserve in an effort to extend the life of the battery pack at the expense of some range. You instead value maximum range, and choose not to. There's no right or wrong here - only choices.

Of course, most will probably return their EV when their lease is up, and lease a new EV with a new battery, so the discussion is largely academic anyway. For some of us however, it does matter. I intend to drive my EV for at least 100,000 miles. Since a replacement battery pack for my car is upwards of $20,000, I choose to take care of it, and will do my best to make it last as long as possible.

 

[michaellax]

What is the possible upside of pushing the battery every night? I sure wouldn't do that

To obtain the maximum range when I need it unexpectedly. Exactly what happened to me last Sunday.

Michael is suggesting what's best for the long term health of the battery based on his own experience and scientific research he's gathered and posted in other threads. You're certainly free to fully discharge / fully charge / and leave your car plugged in all the time to obtain the maximum range when you need it. Most people do exactly that however studies have shown that practice has long term detrimental effects on the battery.

That would not be the case [long term detrimental effects on the battery] if there is sufficient reserve at the top and bottom of the battery.

 

[NeilBlanchard]

I wouldn't trust that number then. The 8.16 kWh are what is delivered to the car. Some of that goes to charging inefficiency, and some of it quite possibly goes to thermal management. The energy actually added to the battery is somewhat less that that number and that's what counts.

280/316 = 89%, much more in line with the commonly cited 10% value.

It was in the upper 50's I think, or maybe the lower 60's - so I doubt that any thermal management was needed. And I think the Bolt EV has very low wall-to-wheels loss - less than 10% and maybe only 8%, so the charging part is half OR LESS of that.

 

[michael]

I wouldn't trust that number then. The 8.16 kWh are what is delivered to the car. Some of that goes to charging inefficiency, and some of it quite possibly goes to thermal management. The energy actually added to the battery is somewhat less that that number and that's what counts.

280/316 = 89%, much more in line with the commonly cited 10% value.

It was in the upper 50's I think, or maybe the lower 60's - so I doubt that any thermal management was needed. And I think the Bolt EV has very low wall-to-wheels loss - less than 10% and maybe only 8%, so the charging part is half OR LESS of that.

Where did you get that wall-to-wheels efficiency number? Battery charging efficiency of 90% would be great, walls to wheels far less I'm pretty sure since that includes the drive systems, not just the battery.

However, discussing electrical efficiencies

Referring to Spark and Volt as examples...

https://avt.inl.gov/sites/default/files/pdf/fsev/fact2015chevroletspark.pdf

Spark has

Battery round trip efficiency 95%
Onboard charger efficiency 83%
Overall electrical efficiency (not including drive motor, etc, just wall to battery) 79%


Volt does much better, however

https://avt.inl.gov/sites/default/files/pdf/phev/fact2016chevroletvolt.pdf


Battery round trip efficiency 99%
Onboard charger efficiency 90%
Overall electrical efficiency (not including drive motor, etc, just wall to battery) 90%

So let's accept that Bolt's electrical efficiency could be 90 %....I believe it will be lower than that in the final stages of charging (since that's when a lot of heating occurs). So I still wouldn't trust the 8.16 number as the amount of extra energy added...I still think it's somewhat less and don't know by how much.

 

[michael]

The obvious solution that is yet to be implemented is to have an Emergency Reserve that has to be manually activated by the driver, like the Reserve position on motorcycle petcocks. This would allow for emergency use of most of the reserved capacity, without the extra stress on the pack from constant use of the last few KWHs.

Hopefully they did that as well in their effort to secure the highest possible EPA mileage rating. Hopefully the allowed us to draw down the battery as much as they think is safe. There is no requirement that you drive it til it stops. You can choose to impose your own minimum SOC level any time you want, and to take it down to the bottom only when circumstances require.

 

[michael]

Well until GM actually makes a statement about the issue, we are debating about how many angels can dance on the head of a pin!

And none of the three of you (not referring to Sean, who posted in the middle of my drafting) have any skin in the game; and I only have a limited amount; so although you are entitled to your opinion, it is of limited value because, so far, none of the three of you have put your money where your mouth is vis-a-vis purchasing a Chevy Bolt EV!

And listening to this advice actually hurt me this weekend, as I started to not plug my Bolt EV in every night and decided at the last minute to take a drive to Moreno Valley Sunday and back, without a full charge!

And although I had a Mileage Gauge indication of 89 miles remaining to come home and probably could have made it "on electrons" I used the EVGo in Moreno Valley for 30 minutes just to be safe; a needless delay had I had my full charge when I began!

Right and I agree this would have been a perfect opportunity to top off the charge before going had time permitted. However, if you choose to fully charge regularly when you don't need to, a few years down the line you may find that you can't make that trip even with a full charge due to battery fade. That's the risk you are choosing to take.

And for the record... while I chose a Volt over a Bolt, my lady friend, on my advice, DID get a Bolt which I drive and rely on regularly (she didn't have the seat comfort issues I did and needed the back seat room). So while I don't make the payments on the Bolt, I have as much interest in its well being and longevity as I would if I did. Maybe more since I'll never hear the end of it if there are problems down the line.

 

[michaellax]

Right and I agree this would have been a perfect opportunity to top off the charge before going had time permitted. However, if you choose to fully charge regularly when you don't need to, a few years down the line you may find that you can't make that trip even with a full charge due to battery fade. That's the risk you are choosing to take.

No, not a risk, but getting the full benefit of the bargain that I made when I obtained the Bolt EV in the first place!

If your scenario holds true, then I am sacrificing the mileage then, that you want me to sacrifice voluntarily now!

And for the record... while I chose a Volt over a Bolt, my lady friend, on my advice, DID get a Bolt which I drive and rely on regularly (she didn't have the seat comfort issues I did and needed the back seat room). So while I don't make the payments on the Bolt, I have as much interest in its well being and longevity as I would if I did. Maybe more since I'll never hear the end of it if there are problems down the line.

You mean like: "I told you so!" hahahahaha :lol:

 

[oilerlord]

That would not be the case [long term detrimental effects on the battery] if there is sufficient reserve at the top and bottom of the battery.

I agree. If there is sufficient reserve. To that point, the term "sufficient" is highly subjective, and may not fit everyone.

To some, having a sufficient battery reserve / buffer may be result of experiencing little to no battery degradation after 3-years / 36,000 miles. For others looking to drive their cars 5-years / 80,000+ miles, they may be willing to accept sacrificing some range to have a larger (sufficient) reserve for the long term. Keeping the SOC below maximum either by limiting the charges manually or through Hilltop Reserve helps to accomplish the latter.

 

[michaellax]

Again, you drivers of vehicles other than the Bolt EV want to debate how many angels will dance on the head of a pin!

I don't need it to fit everyone!

"Some... others...."

I only need it to fit my Bolt EV!

 

[michael]

Right and I agree this would have been a perfect opportunity to top off the charge before going had time permitted. However, if you choose to fully charge regularly when you don't need to, a few years down the line you may find that you can't make that trip even with a full charge due to battery fade. That's the risk you are choosing to take.

No, not a risk, but getting the full benefit of the bargain that I made when I obtained the Bolt EV in the first place!

If your scenario holds true, then I am sacrificing the mileage then, that you want me to sacrifice voluntarily now!

And for the record... while I chose a Volt over a Bolt, my lady friend, on my advice, DID get a Bolt which I drive and rely on regularly (she didn't have the seat comfort issues I did and needed the back seat room). So while I don't make the payments on the Bolt, I have as much interest in its well being and longevity as I would if I did. Maybe more since I'll never hear the end of it if there are problems down the line.

You mean like: "I told you so!" hahahahaha :lol:

I don't care if you sacrifice mileage now or later, but the point is if you waste battery life now you can NEVER get it back. Not like there's something to fix. It's gone forever.

And not "I told you so" since she didn't. More like "You POS. You steered me wrong. Why didn't you recommend a Prius or something normal..."

 

[michaellax]

I don't care if you sacrifice mileage now or later, but the point is if you waste battery life now you can NEVER get it back. Not like there's something to fix. It's gone forever.

And not "I told you so" since she didn't. More like "You POS. You steered me wrong...."

Michael: you and I are going to BOTH lose battery capacity "later"... Time eats ALL battery capacity!

You are giving me advice on a car with no solid proof to back up your claims that I am wasting battery life NOW. But if I follow your advice, I know that I voluntarily gave up that use!

It is YOUR belief that my charging habits caused it to be gone forever; not the mere passage of time!

In the absence of proof, I am going to use the capacity that I paid for NOW, and not piss it down the drain and hope you are correct.

Since the seats are not an issue for her, she couldn't possibly NOT like having a Bolt EV (excuse the double negative for effect) until she sees the next generation EV and she wants that one instead!

So she will only be pissed if you convinced her to purchase and not lease.