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Discussion Starter · #1 ·
So Elon Musk twitted and said in this video:



that the % SOC 90>10 is the recommendation for the lithium-ion battery each day or keep at SOC @ 90% each night, the degradation of the battery is so minimal that you wont able to notice if you are doing 80>30 or 70>30
I would assume we are using the same lithium-ion just like Tesla? because im planning to plugin each night @ 90% to see if i get any degradation.
 

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I think it means that there is an issue with the Model 3's BMS not properly cell balancing at below a certain percentage, but that doesn't change the fact that lithium batteries degrade the least between 40% and 70% state of charge.

What will be interesting is whether Bolt EV (2019+), e-Niro, and Kona Electric owners who set the max battery charge to 70% or lower see the same issue over time. If they don't, then the issue is definitely isolated to Tesla.
 

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I'm keeping my Bolt between 80%-20% as much as possible. That was the usable range in the Volt and those battery packs have held up tremendously over hundreds of thousands of miles. Granted, the software will slowly allow the car to eat into those buffers as the cars age, but to still get the EPA estimated 38 AER in a Volt with over 400,000 miles is a feat of battery technology imo.
 

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Discussion Starter · #5 ·
so with our bolt, the recommend optimal SOC is 80% > 20%? or 80% each night regardless...

Thanks

I have Model 3 and Bolt for my wife, what i experienced on M3 is that when charging at 100%, we will get EPA estimated 310miles or around 306miles (only 2000miles on the car)
But with bolt when we go at 100%, it never hit the mark 255 mi EPA estimated and we are at (14k miles on bolt). I was wondering if its due to the way we charge 80%>20% because in the video it explained clearly that it needs to charge 1 at a month or few weeks at 100% and 90% each night to keep the battery balances and calibrate the miles
Im wondering if our bolt does the same thing too...need to recalibrate using this technique of SOC
 

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so with our bolt, the recommend optimal SOC is 80% > 20%? or 80% each night regardless...

Thanks

I have Model 3 and Bolt for my wife, what i experienced on M3 is that when charging at 100%, we will get EPA estimated 310miles or around 306miles (only 2000miles on the car)
But with bolt when we go at 100%, it never hit the mark 255 mi EPA estimated and we are at (14k miles on bolt). I was wondering if its due to the way we charge 80%>20% because in the video it explained clearly that it needs to charge 1 at a month or few weeks at 100% and 90% each night to keep the battery balances and calibrate the miles
Im wondering if our bolt does the same thing too...need to recalibrate using this technique of SOC
I frequently charge to 100%, and have no issue getting the official Bolt 238 mile range, or more. My understanding is that the range estimate is based primarily on recent driving habits, and not directly related to actual battery capacity.
 

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I frequently charge to 100%, and have no issue getting the official Bolt 238 mile range, or more. My understanding is that the range estimate is based primarily on recent driving habits, and not directly related to actual battery capacity.
I frequently charge to 87% (Hill-Top Reserve) and am delighted to often get 238 miles of range 鈥*if over several days you manage to get about 4.6 miles/kWh each day, the GOM may give you that generous a range. (It's also the case that when I drive downhill to work I see a much more generous number than I see heading uphill to home.)

Spend time driving in the rain and get only 3.6 miles/kWh and you'll see a much more conservative number.

But yeah, @TimBolt's point is the key one. Recent driving is the primary reason why you see your GOM estimate change. GOM stands for guess-o-meter for a reason.
 

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so with our bolt, the recommend optimal SOC is 80% > 20%? or 80% each night regardless...

Thanks

I have Model 3 and Bolt for my wife, what i experienced on M3 is that when charging at 100%, we will get EPA estimated 310miles or around 306miles (only 2000miles on the car)
But with bolt when we go at 100%, it never hit the mark 255 mi EPA estimated and we are at (14k miles on bolt). I was wondering if its due to the way we charge 80%>20% because in the video it explained clearly that it needs to charge 1 at a month or few weeks at 100% and 90% each night to keep the battery balances and calibrate the miles
Im wondering if our bolt does the same thing too...need to recalibrate using this technique of SOC
Here's my opinion. With the Bolt EV, it doesn't really matter. If you don't need the range, only charge it on Hilltop Reserve (up to 88%) or to between 70-80% if you have the Charge Termination feature.

For the Model 3, it sounds like it needs to be charged up every now and then. I'd suggest charging it to 95% to 100% every week or so, but unplug it and take it out for a drive immediately after it finishes charging. In other words, don't just let it sit at 95% to 100% for long periods of time.
 

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Here's my opinion. With the Bolt EV, it doesn't really matter. If you don't need the range, only charge it on Hilltop Reserve (up to 88%) or to between 70-80% if you have the Charge Termination feature.

For the Model 3, it sounds like it needs to be charged up every now and then. I'd suggest charging it to 95% to 100% every week or so, but unplug it and take it out for a drive immediately after it finishes charging. In other words, don't just let it sit at 95% to 100% for long periods of time.
My understanding is that your last piece of advice (in bold) holds true for any EV battery pack, not just Model 3.
 

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That contradicts with what Elon and Tesla has said in the past as stated in the video.

IMO this new "90% is fine" line is due to an issue with the Model 3 BMS that I suspect will be addressed soon. Essentially they are saying something that's not strictly true (though is legally justifiable) to solve a problem.

Also worth noting that Teslas use a different battery chemistry, packaging and BMS than the Bolt. Additionally the Model 3 and Model S/X use different battery chemistry and packaging from each other, though not as different as the Bolt.

FWIW I've gone as long as 1200 miles between "full" (Hill Top Reserve) charges on my Bolt and did not see the cells get particularly unbalanced. Though I don't know at what point in the charge cycle that cell balancing begins so it's possible that I got some balancing the couple times I got up to ~85% SoC in that period.
 

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FWIW I've gone as long as 1200 miles between "full" (Hill Top Reserve) charges on my Bolt and did not see the cells get particularly unbalanced. Though I don't know at what point in the charge cycle that cell balancing begins so it's possible that I got some balancing the couple times I got up to ~85% SoC in that period.
I think I've charged our Bolt to 100% only four times in the year we've owned it (we live at 1950 ft and my work is at 1250 ft, so I gain 700 feet on the way to work each morning and then pay it back driving home, plus I like getting full regen from the moment I set out). So I'd guess that there have been months and at least a few thousand miles between charges to full. It's also almost never very empty. Probably been below 30% fewer than four times.

I'm pretty much 100% certain that the Bolt does a nice taper off that includes battery balancing in hill-top reserve exactly the same as it would when charging to 100%.
 

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Batteries are usually top balanced, meaning balancing is done near 100% SoC. Less common, batteries are bottom balanced near the lower end of their useful SoC. There's also active balancing which I suppose could be done at any SoC, but I haven't heard of this being implemented in EVs.

The balance method isn't discussed anywhere that I've found yet, but my hunch is the Bolt uses top balancing, which means it wouldn't balance when hilltop reserve is used. That said, it probably doesn't make that big of a difference, and occasional full charges to balance would correct any accumulated imbalances.

I'd be curious to learn how the Bolt does balancing, but in everyday use, it probably doesn't matter much if we are charging to full or not.
 

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Batteries are usually top balanced, meaning balancing is done near 100% SoC. Less common, batteries are bottom balanced near the lower end of their useful SoC. There's also active balancing which I suppose could be done at any SoC, but I haven't heard of this being implemented in EVs.
I'm certainly no battery engineer, but since "fully charged" is basically an arbitrary number that the engineers set to allow a margin below which the battery starts to be damaged, I imagine that the batteries could be balanced at any state of charge. It's basically just a matter of monitoring the voltage level of the individual modules and switching them in and out of the charging loop until they all read the same, isn't it? The only issue would be that it takes time to to the balancing, but that's why you wait until the batteries reach their target charge level (be that 60%, 80% or whatever).

The only issue that seems obvious to me is that balancing them at, say, 80% charge level may not result in a battery that's properly balanced if you later charge it to 100% . But if you rebalance when you reach that level anyway then that doesn't seem like it would be a real problem.
 

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I think I've charged our Bolt to 100% only four times in the year we've owned it
I've had my Bolt 10 months and only charged to 100% once, by accident; I had disconnected the 12v battery when I went away on a trip for a few weeks and did not realize that when you do this that HTR gets turned off.

For me a "full" charge is with HTR so ~90%. But I nearly always interrupt the charge and unplug at about 80%. I intend to charge to "full" (HTR) about every 1000 miles just for the cell balancing benefit. My last time I went to 1200 miles.

If I had the target charge setting on my car I'd set it to 75% and just plan on charging once a week and not worry about it.
 

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Batteries are usually top balanced, meaning balancing is done near 100% SoC. Less common, batteries are bottom balanced near the lower end of their useful SoC. There's also active balancing which I suppose could be done at any SoC, but I haven't heard of this being implemented in EVs.

The balance method isn't discussed anywhere that I've found yet, but my hunch is the Bolt uses top balancing, which means it wouldn't balance when hilltop reserve is used. That said, it probably doesn't make that big of a difference, and occasional full charges to balance would correct any accumulated imbalances.

I'd be curious to learn how the Bolt does balancing, but in everyday use, it probably doesn't matter much if we are charging to full or not.
I've read on here that the Bolt does do cell balancing at/near the end of a HTR charge just like a "100%" charge.

I could probably verify this by looking back at my torque logs and seeing if the cells are noticeably more balanced after having charged to "full" (HTR) after having driven more than 1200 miles since the last "full" (HTR) charge and more than 2500 miles since the one and only "100%" charge I've done since I've owned it.
 

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For me a "full" charge is with HTR so ~90%. But I nearly always interrupt the charge and unplug at about 80%.
Hill-top reserve is a tad over 87%. The likely difference you'll see in battery life from saving 6 or 7% is almost certainly so negligible that you'll never be able to detect it, and it may be outweighed by not allowing the car to balance the batteries.

On the one hand, I'm all for live and let live 鈥 if you think depositing a fried egg on each tire every morning will improve your grip and help them last longer, it's totally your right to do that. On the other hand, there are a lot of folks out there who are somewhat nervous about buying an EV 鈥*I'd hate for anyone to think that these kinds of battery-babying rituals are necessary or widely performed.
 

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It's basically just a matter of monitoring the voltage level of the individual modules and switching them in and out of the charging loop until they all read the same, isn't it?
No, it isn't. The 96 cells (actually three in parallel, but paralleled cells are functionally one cell) are all wired in series, with the current running through the entire series. There is no practical way to pull a cell out of a series. It would require heavy duty relays, and lots of extra heavy duty busbars to switch out a cell and bypass it. And the charging voltage of the rest of the cells in the remaining series would have to be reduced to maintain the correct charging current level. It would be an expensive, heavy, complicated, failure prone nightmare.
 
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