Hilltop Reserve

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NeilBlanchard

Well-known member
Joined
May 31, 2016
Messages
337
Location
Massachusetts
I measured what the "hilltop reserve" is on the Bolt EV - about 8.1kWh or so. Which is about 1/3rd the total capacity of Leaf 24kWh and the e-Golf - which is pretty amazing.

I also learned that if you leave the charge port door open, the main screen in the car doesn't work. I had a moment of panic, but it is good to know.
 
Wow, that's almost 15%. I thought it was only 10%. How did you measure it?

I'm more interested in Hilltop Reserve for being gentler on the battery. I don't need anywhere near the Bolt's full range most days, and it is more gentle not to charge to full. I know the Bolt is engineered to protect its battery and all, but I hope to keep mine for a long time. I want the battery to last 10-15 years, while still providing 200+ miles/charge.
 
I have the impression it's more than 10%, although I wouldn't depend on that unless we get more info.

Typically I show 250 miles fully charged and around 200 on hilltop but of course there is day-to-day variation so it's hard to pinpoint
 
GetOffYourGas said:
...I'm more interested in Hilltop Reserve for being gentler on the battery. I don't need anywhere near the Bolt's full range most days, and it is more gentle not to charge to full. I know the Bolt is engineered to protect its battery and all, but I hope to keep mine for a long time. I want the battery to last 10-15 years, while still providing 200+ miles/charge...
Ditto. I do the same thing. I purchased the car and hope for 10+ years of battery.
The app shows 87% when "fully charged" (hilltop reserve)
 
GernBlanston said:
GetOffYourGas said:
...I'm more interested in Hilltop Reserve for being gentler on the battery. I don't need anywhere near the Bolt's full range most days, and it is more gentle not to charge to full. I know the Bolt is engineered to protect its battery and all, but I hope to keep mine for a long time. I want the battery to last 10-15 years, while still providing 200+ miles/charge...
Ditto. I do the same thing. I purchased the car and hope for 10+ years of battery.
The app shows 87% when "fully charged" (hilltop reserve)

Agreed. Most of the trips in our Bolt are short. We charge on Sunday and often go a week, sometimes more before charging. We take it out of Hilltop Reserve to go on round trips that will take us beyond the car's listed range. Even in Hilltop Reserve mode the mid-range estimator shows 220 miles of range.
 
mrp10000 said:
...Even in Hilltop Reserve mode the mid-range estimator shows 220 miles of range.
Yeah, I'm getting 200-240 depending on the temps. Charging twice a week under normal circumstances.
 
I'm VERY disappointed that Nissan didn't copy GM on this, and offer a similar mode. (They got burned by the EPA in 2013 when they offered an 80% charge mode and got a revised EPA range estimate as a result.) So anyone driving a 2018 Leaf will have to limit the charge manually. So damned stupid...
 
NeilBlanchard said:
I also learned that if you leave the charge port door open, the main screen in the car doesn't work. I had a moment of panic, but it is good to know.

Good to know, thanks. So, we can't play with screen while charging? That's no fun. Wonder if it can hacked by jimmying the hatch switch.
 
Does anyone know if the Bolt can be coded (has anyone?) to change the Hilltop mode to only charge to 80%, or if there's another way to do this? This is the optimal charge level for battery longevity and has been recommended by battery experts. EV batteries should be charged only to about 80% regularly unless a long trip is planned where more battery capacity is needed.
 
The getaround I use is to charge to hilltop, and set the charge timer to end up around 7 AM. That way the battery stays at even the hilltop level for only a short time before I (usually) drive somewhere and pull it down a little.

I know it would be better to stop the charge at some lower level, but they haven't made that easy. Every manufacturer should provide a slider like Tesla does.

I have fully charged only once, before taking my first 140 mile trip. When I found the car worked as expected and still had nearly 100 miles left, I gained the confidence in the range estimate and switched to perma-hilltop
 
brorob said:
Does anyone know if the Bolt can be coded (has anyone?) to change the Hilltop mode to only charge to 80%, or if there's another way to do this? This is the optimal charge level for battery longevity and has been recommended by battery experts. EV batteries should be charged only to about 80% regularly unless a long trip is planned where more battery capacity is needed.
What we really need is to know what "87%" and "100%" on the meter mean relative to the actual capacity of the battery pack.
With a little luck, our hilltop reserve top-off puts the battery at, say, 80% of the total capacity when it reaches 87% of the usable capacity,
putting us right in the sweet spot for battery longevity without having to game the system to get the charge level that we want.
(Hey, I'm a glass-is-half-full kinda' guy.) :)
 
80% SOC isn't actually the 'optimal' charge for longevity. That would be more like 40%. 80% is a compromise between longevity and having enough range available.
 
LeftieBiker said:
80% SOC isn't actually the 'optimal' charge for longevity. That would be more like 40%. 80% is a compromise between longevity and having enough range available.

Right. 40% is optimal for most lithium batteries. 80% is the point where the stress starts growing very quickly. If you look at the voltage-vs-charge curve for lithium batteries, the voltage starts shooting up quickly above 80%. This is what causes the extra stress on the battery.

I'm just glad that GM provided the hilltop reserve mode. By calling it that, they can circumvent the EPA range de-rating nonsense. Nissan's mistake was calling the 80% the "recommended" setting. I have to put more faith in the average person to know that an 80% charge will not get you as far as a 100% charge. But I guess the EPA thinks we are all idiots.
 
This may be a dumb question and/or answered somewhere else...does anyone know what the total vs usable capacity is for the Bolt's battery pack? Assuming the usable capacity really is 60 kWh, is the total capacity 65 kWh? 70 kWh? Just wondering if anyone knows how much buffer GM engineered into the battery pack.
 
oilerlord said:
This may be a dumb question and/or answered somewhere else...does anyone know what the total vs usable capacity is for the Bolt's battery pack? Assuming the usable capacity really is 60 kWh, is the total capacity 65 kWh? 70 kWh? Just wondering if anyone knows how much buffer GM engineered into the battery pack.
Would love to know, but I don't think anyone at Chevy's talking.
 
GernBlanston said:
oilerlord said:
This may be a dumb question and/or answered somewhere else...does anyone know what the total vs usable capacity is for the Bolt's battery pack? Assuming the usable capacity really is 60 kWh, is the total capacity 65 kWh? 70 kWh? Just wondering if anyone knows how much buffer GM engineered into the battery pack.
Would love to know, but I don't think anyone at Chevy's talking.

No, GM has not disclosed this number, however a lot of research results posted on this and other EV forums guesstimates it at 64 kWh - about a 6% ceiling. I think a lot of these calculations came from some math applied to the number and size of each cell that make up the battery pack.
 
I think they pushed it pretty hard. Normal practice in the industry is to claim the battery capacity based on the full capacity, not the capacity used. So I think the 60 kWh usable we are seeing corresponds reasonably closely to the rated capacity of the pack. But I don't know that as a fact...until someone like INL runs a test on the isolated battery pack, this will just be guesswork on my part
 
GetOffYourGas said:
Wow, that's almost 15%. I thought it was only 10%. How did you measure it?

I'm more interested in Hilltop Reserve for being gentler on the battery. I don't need anywhere near the Bolt's full range most days, and it is more gentle not to charge to full. I know the Bolt is engineered to protect its battery and all, but I hope to keep mine for a long time. I want the battery to last 10-15 years, while still providing 200+ miles/charge.

I measured it by charging in Hilltop Reserve, then unplugging it, then toggling off Hilltop Reserve, and then plugging it in again. My JuiceBox Pro 40 has an app that displays the charge. The precise number was 8.16kWh for the top off charge.

Oh, the range indicated with the Hilltop Reserve on this instance was 280 miles, and it was (about) 316 miles with at full charge. (I asked my spouse what the average range was, and she had already driven it a little bit.) We are averaging 5.1 miles / kWh over about 1200 miles that we have driven so far. A fair bit of that is at highway speeds.
 
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.
 
Patronus said:
GernBlanston said:
oilerlord said:
This may be a dumb question and/or answered somewhere else...does anyone know what the total vs usable capacity is for the Bolt's battery pack? Assuming the usable capacity really is 60 kWh, is the total capacity 65 kWh? 70 kWh? Just wondering if anyone knows how much buffer GM engineered into the battery pack.
Would love to know, but I don't think anyone at Chevy's talking.

No, GM has not disclosed this number, however a lot of research results posted on this and other EV forums guesstimates it at 64 kWh - about a 6% ceiling. I think a lot of these calculations came from some math applied to the number and size of each cell that make up the battery pack.
michael said:
I think they pushed it pretty hard. Normal practice in the industry is to claim the battery capacity based on the full capacity, not the capacity used. So I think the 60 kWh usable we are seeing corresponds reasonably closely to the rated capacity of the pack. But I don't know that as a fact...until someone like INL runs a test on the isolated battery pack, this will just be guesswork on my part
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!
 
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