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Newb here. Have twice charged the (brand new, <200 miles so far) Bolt 'til instrument panel says charged, light on dashboard is solid green, and Juicebox charging system shuts down normally (also happened with the factory 110v charger). But the infographic display shows the leftmost two cells grayed out. Any idea what's up with that? Thanks.
 

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Hmmm, that's an interesting observation. I'll have to take a look at mine next time. You wouldn't by chance have Hill Top Reserve (HTR) turned on, would you? HTR limits your max charge to 90% of your 60 kWh battery, which matches nicely with your picture: 18/20 bars is the same as 90/100.
 

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So what is this "Hilltop reserve" that everyone's mentioning? It's a way to deliberately leave some empty "space" in the battery so that it can accept more charge. This can be important if you live at the top of a hill and you want to be able to recapture braking energy back into the battery as you go down the hill.

If you charged the battery at home so that it's completely full, there would be no room to in the battery to store the energy that could be regenerated as you go down the hill, so you'd have to use the hydraulic brakes instead. That's a waste of the energy you could have potentially recouped.

It's more important if you use "one pedal driving" "(L" mode), since a full battery will prevent you from slowing down as quickly and you'll have to move your foot to the brake pedal on those occasions where you have to stop a bit more quickly.

Another reason to use "Hilltop Reserve" mode is that it's probably a bit less stress on the battery if you don't regularly charge it to it's full capacity. It's generally agreed that a lower charge is easier on the battery and will likely lead to less battery degradation and longer overall lifetime. But just how big a real world difference it will make is anyone's guess right now.
 

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...a full battery will prevent you from slowing down as quickly
That`s not my experience. See below picture showing my ``test`` data. Setting off with battery 100% full and measuring g-force no-brake-pedal L mode (plus paddle) slowing & stopping action. Regen spinner icon is grayed out indicating no energy being returned to battery yet I still pull deceleration up to -0.39g as usual as if I was at or below hilltop reserve charge level. Theory: either my Bolt is malfunctioning, or, the regen energy being generated but not used, is being dissipated as heat by design.

Give it a try ;)
 

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Discussion Starter #8
Ah, good to know. It's all uphill from here, so will experiment. Thanks.
[and at some point start RTFMing....]
 

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or, the regen energy being generated but not used, is being dissipated as heat by design.
Our Bolt seems to regen just fine at 100% charge. But we aren't speeding up to stop signs either. Don't know if the BMS system in the Bolt is like most I am familiar with. If it is, there are resistors which burn off excess energy above 4.2 volts, or, in the case of the Bolt, 4.187 volts per cell. Have you noticed what the regen kW's are when you are pulling these g's? It would be pretty simple to calculate how big the resistors would need to be.
 

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=borkbork;250977]same here. i see people posting about reduced regen, and the regen part might be true, but the deceleration seems the same to me.
Thank you. Good to know. At least I`m not the only one seeing this.

Have you noticed what the regen kW's are when you are pulling these g's? It would be pretty simple to calculate how big the resistors would need to be.
No I didn`t. I only observed the grayed-out regen spinner telling me there`s no juice being restored to the battery. Was too busy keeping the vehicle between the ditches as I was pulling the paddle and taking the G-meter picture at the point when it hit max G`s.

Next time that I charge to 100%. After setting off initially I`ll see if I can read any kW`s during the no-brake-pedal deceleration test.
 

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Regen max is 70 kw. Consider that 93 brake horsepower.
Regen is limited to about 24 kw when you depart with a fully charged battery. So consider that 32 brake horsepower.

However, you may feel the car is behaving normally because 24 kw ( 32 bhp ) is what most people generally use to come to a normal gentle stop.

This power is going into the battery. There are no resistors or more than usual waste heat. The grey regen icon means regen is reduced, not regen is off.

After more than a couple stops on a full battery, regen is reduced again to 16 kw ( 21 bhp ).

I’ve never had regen completey stop in my vehicle. But I do not have a long, sustained downhill area to test.
 

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Just re-read GJeston’s post.

I now understand what he was saying. IE the normal battery balancing resistors. It would be interesting to see if pack temperature goes up more than usual when you regen on a full battery.

My theory is this is a 62-64 kWh pack, where as we use the 60 kWh in the middle and there is a bit of headroom after “100%”.
 

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I live on a hill and normal use hill-top reserve. On one occasion when I didn't, after some down hill travel, the central panel announce battery is full or charge to 100%. At that point, did feel any regen.
 

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Today with battery level about 40% I tried two full-regeneration stops from 60 kph (about 37 mph): deceleration peaked at -0.31g and -0.32g. Time to bring vehicle to a complete stop from 60 kph was 6.5 seconds. Regeneration KW`s peaked at 53KW.

This deceleration fits the range previously observed for this test (see table in post 6) wherein it ranged from -0.28g up to -0.35g when the battery was 100% full. So wouldn`t the amount of available regenerative energy have been about the same that earlier time as well ?
 

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That`s not my experience. See below picture showing my ``test`` data. Setting off with battery 100% full and measuring g-force no-brake-pedal L mode (plus paddle) slowing & stopping action.
That's interesting, but I have no easy way to test it. A good test requires a charge to 100% at the top of an extended hill, and there aren't any chargers around here that fit the bill. I don't trust acceleration/deceleration tests because you have to use juice to get up to speed and that makes room in the battery for the regen created by the deceleration.
 

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Today tested with a hill on a full battery and using cruise control. I could set cruise control initially but as the hill got steeper my regen stopped (icon was grey now, not a spinning green circle) for brief moments and ultimately stayed grey with no regen occuring. The cruise control icon also changed from "green" to "grey" indicating it was no longer maintaining my speed and I was easily gaining 15mph over the speed limit in seconds. When I had used up a green bar of energy (forgot to take note of the kWh used), I came back to the same hill and repeated the cruise control down hill. This time, I regen'd to a max of 40 kWh all the way down the hill. I did have HVAC going at 72F and it was about 50F outside today.

I live on a hill and normal use hill-top reserve. On one occasion when I didn't, after some down hill travel, the central panel announce battery is full or charge to 100%. At that point, did feel any regen.
to remove any ambiguity. you didn't feel any regen?
I wasn't sure if I felt anything when I was manually braking after cruise control disengaged. When I was braking, I didn't focus on the energy bar very well so I don't trust if I saw any additional regen from using the brake pedal. Since I was approaching 15 mph over the limit, I was more focused on braking to reduce speed as quickly and safely as possible. I also was pressing fairly hard on the brake pedal so I don't think I would've felt any transition from regen to friction brakes. Any change in deceleration from such regen-friction switching would've been hard to detect. Only deceleration changes I think I recall were from me modulating the brake medal myself.
 

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Today tested with a hill on a full battery and using cruise control. I could set cruise control initially but as the hill got steeper my regen stopped (icon was grey now, not a spinning green circle) for brief moments and ultimately stayed grey with no regen occuring. The cruise control icon also changed from "green" to "grey" indicating it was no longer maintaining my speed and I was easily gaining 15mph over the speed limit in seconds.
Interesting. Was vehicle in L and paddle pulled ?
 

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Have you noticed what the regen kW's are when you are pulling these g's? It would be pretty simple to calculate how big the resistors would need to be.
Next time that I charge to 100%. After setting off initially I`ll see if I can read any kW`s during the no-brake-pedal deceleration test.
Okay I charged my Bolt up to 100% full battery. Then I drove it gently 1.2 kms (~ ¾ of a mile) to the point where I could safely commence the no-brake-pedal deceleration test. Commencing from 60 km/h (~ 37 mph) until I came to a complete stop. I figure I used up about 0.18 kWh of battery in travelling the 1.2 km to get to the start of the test, so that left me 99.7% full battery at that point. Assuming of course there’s no hidden headroom in the battery.

See below video displaying measurements decelerating from 60 km/h to a complete stop: kW’s peaked at 32 kW, vehicle took 9.6 seconds to come to a complete stop from 60 km/h. I didn’t measure deceleration g’s this time because I couldn’t launch the app at the same time I was taking the video.

Conclusion: As I’ve seen before and confirmed with this latest test. My Bolt readily decelerates in L mode (w/paddle or not) when it’s battery is virtually “full”. However, in this condition the regen capture rate is somewhat restricted: for example in my 60 kph to stop test, I got max of 32 kW with 99.7% full battery, compared to max of 53 kW earlier when my battery was 40%. One can see the restriction level in the video (32 kW in this example) as depicted by a light grey line adjacent to the kW readout on the right hand side of the 8” screen. The time-to-stop is consistent with the kW’s restriction: 9.6 seconds from 60 kph to zero (99.7% battery) compared to 6.5 seconds with 40% battery.

Implication: Since there aren’t many significant hills where I live. The only possible advantage I see with “hilltop reserve” ~89% charging is: avoidance of the battery degradation in the long term ? associated with consistently topping it off. As the theory goes. Otherwise with full charging I can still get L mode deceleration that’s good enough for practical purposes, along with some regen capture. And I get that extra 30 kilometres or so range (net) which is important if I want to do highway driving and/or if it’s a very cold day and I’d like a bit of heat. Soooo…certainly in the winter I’m going to be doing more 100% full charging. To heck with the worry of reduced battery capacity/life in the long term, at least until someone proves that theory.
 
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