[HybridLA]

Curious why the common opinion is to only charge to 80% on a regular basis? If we are not allocated access to the total 111.5kw (as max usable is only 105.2kw) are we not - even at 100% charge of 105.2kw - really only at 94% of max battery size (105.2kw / 111.5kw = 94%)?

By that logic (if not flawed) we should be able to safely charge to 90% of 105.2kw which equals to 94.68kw (90% of 105.2kw). By extension that means we are really only at 85% of total battery size (94.68kw / 111.5kw = 84.9%).

Maybe my logic is all off?

[exxxviii]

If you are leasing, charge to whatever you want.

Conventional guidance is charge to 80%. I charge to 90%. I like that extra 10%.

I don’t charge to 100% because that affects regen and one pedal driving.

[ggalanis]

Originally Posted by HybridLA

Curious why the common opinion is to only charge to 80% on a regular basis? If we are not allocated access to the total 111.5kw (as max usable is only 105.2kw) are we not - even at 100% charge of 105.2kw - really only at 94% of max battery size (105.2kw / 111.5kw = 94%)?

By that logic (if not flawed) we should be able to safely charge to 90% of 105.2kw which equals to 94.68kw (90% of 105.2kw). By extension that means we are really only at 85% of total battery size (94.68kw / 111.5kw = 84.9%).

Maybe my logic is all off?

There are buffers both at the bottom and top of the pack. The useable part of the battery is situated in between them. So in essence, 80% is more charge than 80% of the useable part. If you assume equal buffers of 3.15 kWh on each end, charging to 80% is about 78.5 of the real capacity.... So pretty much 80% anyway. I don't think we know officially what the buffers on each end are like. And of course you can play with the buffer sizes to get that to be exactly 80% if you want.

The reason the common opinion is to go to 80% is because that's what the manufacturer recommends. This is a compromise between usability and long term degredation because in reality, it would be better for the battery to be around 50%. The degredation at something like 80% soc is likely close to negligeable and gives people access to most of their range to help alleviate range anxiety.

[ggalanis]

Originally Posted by exxxviii

I don’t charge to 100% because that affects regen and one pedal driving.

Have you tried this on your iX?

From the few times I went to 100, I never saw the car not able to use regen (to be fair I wasn't testing this specifically so there is always the chance I didn't notice), unlike Teslas who do seem to severely limit regen braking at the top end of the SOC.

[Windshieldfarmer]

When plugging in at home I normally only charge to 80% sice it’s believed to support battery longevity. I see that this is also being recommended for phones also.

I’m not afraid to charge to 100% when driving on trips but I try to leave within several hours of achieving the high charge level. A number of studies suggest battery longevity and capacities are best maintained by keeping charge levels between 10 and 80%. BMW recommends the 80% max in the manual.

I liken this recommendation to oil change intervals on ICE vehicles. I’m sure you can exceed the manufacturer recommendations and probably be ok, but it’s not good for the engine long term.

Even though my IX is a lease, I treat it like an owner and follow the recommendation not to regularly charge over 80%. The short term nature of my daily usage does not make a slight increase in charging frequency inconvenient since I charge in my garage.

[exxxviii]

Originally Posted by ggalanis

Have you tried this on your iX?

From the few times I went to 100, I never saw the car not able to use regen (to be fair I wasn't testing this specifically so there is always the chance I didn't notice), unlike Teslas who do seem to severely limit regen braking at the top end of the SOC.

BMWs use friction braking when it cannot regenerate. Same as Teslas.

[javapro]

Originally Posted by ggalanis

Have you tried this on your iX?

From the few times I went to 100, I never saw the car not able to use regen (to be fair I wasn't testing this specifically so there is always the chance I didn't notice), unlike Teslas who do seem to severely limit regen braking at the top end of the SOC.

Think about it. If your battery is at 100% or close to it, there is no where for the electricity generated by regen braking to go, so the car will not use regen braking. I wonder what’s the threshold is for the regen braking to start working, Is it 98% or 99%? If this threshold is 1 or 2% or may be even 0.5%, then there will be only a very short period of time when regen braking is not engaged.

[darylp310]

I'm just guessing that because BMW is so extremely conservative, they leave a large buffer even after you charge to 100%. Remember the actual battery size is 111.5 kWh and we can only charge up to 105 kWh.

I've charged to 100% a few times, and I've never seen regen not work, and I've never seen a warning message in my iX either. When I've driven the Tesla Model X and the Ford Mustang Mach-E I've seen a "Using Physical Brakes" error message several times when trying to brake at or near 100%.

I wonder if this is the difference?

[javapro]

Originally Posted by darylp310

I'm just guessing that because BMW is so extremely conservative, they leave a large buffer even after you charge to 100%. Remember the actual battery size is 111.5 kWh and we can only charge up to 105 kWh.

I've charged to 100% a few times, and I've never seen regen not work, and I've never seen a warning message in my iX either. When I've driven the Tesla Model X and the Ford Mustang Mach-E I've seen a "Using Physical Brakes" error message several times when trying to brake at or near 100%.

I wonder if this is the difference?

Yes but remember that the car’s software forces it to think that all it has available is the usable capacity. The bottom and top buffers are off limits! Basically the car is not allowed to discharge the battery to 0% of total capacity as well as charge it to 100% of total capacity.

[ggalanis]

Originally Posted by exxxviii

BMWs use friction braking when it cannot regenerate. Same as Teslas.

Originally Posted by javapro

Think about it. If your battery is at 100% or close to it, there is no where for the electricity generated by regen braking to go, so the car will not use regen braking. I wonder what’s the threshold is for the regen braking to start working, Is it 98% or 99%? If this threshold is 1 or 2% or may be even 0.5%, then there will be only a very short period of time when regen braking is not engaged.

That's one of the uses of the top buffer, which is why i specifically asked if exxxviii tried it on his iX. As far as i remember, even at 100% the car will still do 1 pedal driving without friction brakes, and still use regen as before when you press the brake pedal. As far as I know Tesla doesn't use a top buffer and the fact they have to limit Regen at the top end of the SOC is one indication of this.

[ggalanis]

Originally Posted by javapro

Think about it. If your battery is at 100% or close to it, there is no where for the electricity generated by regen braking to go, so the car will not use regen braking. I wonder what’s the threshold is for the regen braking to start working, Is it 98% or 99%? If this threshold is 1 or 2% or may be even 0.5%, then there will be only a very short period of time when regen braking is not engaged.

It isn't just about having the capacity for the energy, but at the top end of the SOC, you cannot charge as fast just like when you use a DCFC. So at some point near a true 100% you can't send a high power regen spike back into the pack without potentially damaging it. Cars with a top buffer can allow you to send that big spike just because they aren't truly at their limits yet. Of course don't expect to regen down a mountain starting with 100% at the top... You will eventually hit the limit in any EV no matter how much top buffer they put in there.

[darylp310]

Maybe we just have to give props to BMW for making physical braking and regen braking so smooth and similar that I could never tell the difference. In the Tesla and the Ford I could tell right away when the physical brakes were being applied.

[ggalanis]

Originally Posted by darylp310

Maybe we just have to give props to BMW for making physical braking and regen braking so smooth and similar that I could never tell the difference. In the Tesla and the Ford I could tell right away when the physical brakes were being applied.

They did blend them very well, but the screen shows you the amount of regen and you can still tell the difference when the car is about to stop (and in slippery conditions which would normally activate the abs system).

[liquidator4711]

Originally Posted by exxxviii

BMWs use friction braking when it cannot regenerate. Same as Teslas.

Maybe newer Teslas, but my current Tesla P85D from 2015 has zero regen when charging to 100%. Looking forward to the iX in less than a month now…

[exxxviii]

Originally Posted by ggalanis

That's one of the uses of the top buffer, which is why i specifically asked if exxxviii tried it on his iX. As far as i remember, even at 100% the car will still do 1 pedal driving without friction brakes, and still use regen as before when you press the brake pedal. As far as I know Tesla doesn't use a top buffer and the fact they have to limit Regen at the top end of the SOC is one indication of this.

I have driven my car at 100% only once, and it was just a short distance. There was not an opportunity to objectively discern the degree to which it might have been blending its friction braking to simulate full OPD regeneration.

I do not know of a test that can conclusively prove it one way or another. When the battery is at 100% charge, it cannot regenerate, because the energy has no place to go. When a battery is close to 100%, it can regenerate, but at a diminished level, because current intake is constrained at high states of charge.

I think BMW shows an indicated 100% SoC when it is actually a little below 100%. It could be as low as 92%, based on Consumer Reports' range test.

[thebishman]

I don’t think this is Apples to Oranges even though the battery chemistry might be slightly different, but I routinely charged my ‘19 etron to 90% SoC the vast majority of the time. Many times I also charged it to 100%. When I sold the car, the range at 100% was no different than the day I drove it off the lot; (in fact it was about 10 miles greater because Audi had performed an efficiency upgrade to all early model year eTrons).
Caveat: my etron never saw a DCFC charger, it was only ever L2 charged at home on my ChargePoint Flex which runs at 32A continuous.
My point is that I believe manufacturers are incredibly cautious re: how high we should routinely charge the HV battery to, but that on a typical L2 home type charger you are not hurting the battery by charging to 90% routinely or certainly 100% on occasion especially if that 100% charge occurs right before drive off.

[ggalanis]

Originally Posted by exxxviii

I do not know of a test that can conclusively prove it one way or another.

I know of 2 ways other than looking at the dash to see the regen level which in theory could be faked but I don't see why they would do that.

First way, there is a different feeling when reaching the end of a braking sequence coming to a full stop in D mode and using one pedal driving in B mode. In D mode, the friction brakes will do the last bit of braking and you can get them to be noisy (i.e. making flatulent noises) if you apply just the right/wrong amount of brake pressure. When using B mode, you get absolutely none of this. The car seems to engage the brake only once fully stopped (if at all).

The second way, on slippery (i.e. icy) roads where the car would slip under the braking level offered via regen, the car does an excellent job at modulating the regen brakes fast to avoid locking a wheel. This does not use the ABS pump and thus you don't get the typical vibration in the brake pedal you do if you were using the friction brakes. I noticed this a while back and I think posted about it at the time as well because it makes it harder to test how slippery the roads are in winter. On ABS equipped vehicles without regen braking, you could basically do a quick brake test and see how much it takes to activate the ABS system. The regen masks this effect in the iX unless you brake much harder and can give drivers a false sense of how much traction is actually available. Instead, you have to be more in tune with feeling if the car is wiggling at all at braking levels below the regen/friction brake threshold.

Originally Posted by exxxviii

I think BMW shows an indicated 100% SoC when it is actually a little below 100%. It could be as low as 92%, based on Consumer Reports' range test.

I concluded a while back that they do indeed use a top buffer. This is one of the benefits of using one. For almost all users, this ensures they will never feel anything different with their regen. I assume anyone actually bringing the car SOC over the displayed 100% will eventually trigger an error in the car warning the user that their regen is limited and that the limitation would be graphically displayed on the dash just like the power limit is when the car is too cold. I don't hate myself enough to drive in winter without preconditioning it most of the time so I don't think I've ever had the battery so cold that even regen was limited (I think I may have seen it once but I wasn't paying close attention and think it may be a figment of my imagination so I wouldn't count it as having seen it). I've barely seen the power limit a couple of times for sure.

[ggalanis]

Originally Posted by thebishman

My point is that I believe manufacturers are incredibly cautious re: how high we should routinely charge the HV battery to, but that on a typical L2 home type charger you are not hurting the battery by charging to 90% routinely or certainly 100% on occasion especially if that 100% charge occurs right before drive off.

Some companies are indeed incredibly cautious. I count BMW in that conservative group. Going up to a high SOC on a slow charger removes one of the issues which is heat, but it doesn't remove the issue batteries have with not "liking" to be at high SOC for long periods of time.

It is hard/impossible to get real accurate numbers on what this represents in terms of degradation, but even 80% causes some unnecessary degradation because it strays from the ideal SOC that packs "like" to be at which is apparently more like 50%. Quantifying what that extra damage is is very difficult and it is likely negligible in the grand scheme of things. Regularly exceeding 80% when not needed does more long term damage but again, I haven't seen anyone quantifying it and I would expect it to be minimal if not negligible. However manufacturers seem to have converged to around 80% being the right daily charge % considering the tradeoffs involved.

With all this said, I have no issues charging to 100% when I expect to need it or even if I expect to need only 70% and want the extra buffer. Just like I won't hesitate to use a DCFC whenever I need to on a long trip.

[Paladin1]

Originally Posted by javapro

Yes but remember that the car’s software forces it to think that all it has available is the usable capacity. The bottom and top buffers are off limits! Basically the car is not allowed to discharge the battery to 0% of total capacity as well as charge it to 100% of total capacity.

This. In brief, the iX battery is a large, expensive (on the order of $80-90k), difficult to replace li-ion battery (actually a lot of them, connected). Li-ion batteries eventually lose their capacity to retain a charge (degrade), a chemical process that is unstoppable due to the nature of the battery. This process is rate-dependent, and occurs with normally discharging it as intended, charging it, and speeds up in extremes (outside the nominal operating temperature) of heat and cold. Degradation also proceeds faster if the battery is continuously charged to its maximum capacity, or discharged until its output is zero current or near zero.

Manufacturers and engineers have cleverly designed techniques to mask the degradation rate by conserving part of the battery's capacity at the low end (the part of the battery when it chemically first begins to recharge), and the high end (that part of the battery that chemically recharges last). This is generally coupled with some sort of electronic indicator that tells the end user when the battery has reached "0% capacity," and "100% capacity." Each of these readings is not actually 0, and not actually 100, depending on the design. The difference is called the "buffer." So when the indicator reads 0, the actual remaining capacity may be 5, 10, 15%, etc., again depending on design. When the indicator reads 100%, the actual capacity may be 85, 90, 95%, etc. The electronic indicator is also associated with some sort of automatic cutoff - when the indicator reads 0%, the device will shut down and stop removing power from the battery. When the indicator reaches 100%, the battery will stop the chemical recharge process.

This does three things - it prevents the battery from actually completely discharging - true 0% - which will sometimes render a li-ion battery unrecoverable, and it prevents it from reaching its chemical capacity to recharge - true 100% - which will ultimately reduce the power it can deliver when fully charged - or degrade. It also allows the in-between capacity - or "usable" capacity - to "borrow" from the high and low end capacity over the life of the battery to mask the fact that the battery overall has lost capacity. In other words, even though the battery may have lost 5% of its ability to hold a maximum charge, the usable capacity is close to its original performance because it will use capacity from the buffer - up to a point.

That's why the battery in the iX can be warranted for 8 years, with less than a 30% reduction in capacity. And it's probably going to be a lot less, although we haven't reached the 8 year point in any of them. If you could fully use the buffer all of the time, that degradation would occur faster so nothing to be gained, and potentially more issues with charging and unrecoverable - expensive - batteries.

*To address the original question, you probably could charge to "100%" most - or all - of the time AC charging and not see a significant increase in capacity loss. It's just BMW being conservative (although leaving the battery at 100% state of charge increases the rate of reaction in the battery versus 80%, or 70%, or 60%, and an increased reaction rate means increased degradation, potentially significantly). OTOH, charging to 100% on a DC charger exposes the battery to more heat, potentially a lot more over a longer time, hence faster degradation, in addition to the increased charging time over about 80% (possibly double). Rather than explain in detail "this is when you should charge to 100%, this is when you shouldn't," BMW has just used a blanket, and safe, 80% "unless you need to" statement.

[javapro]

Originally Posted by Paladin1

This. In brief, the iX battery is a large, expensive (on the order of $80-90k), difficult to replace li-ion battery (actually a lot of them, connected). Li-ion batteries eventually lose their capacity to retain a charge (degrade), a chemical process that is unstoppable due to the nature of the battery. This process is rate-dependent, and occurs with normally discharging it as intended, charging it, and speeds up in extremes (outside the nominal operating temperature) of heat and cold. Degradation also proceeds faster if the battery is continuously charged to its maximum capacity, or discharged until its output is zero current or near zero.

Manufacturers and engineers have cleverly designed techniques to mask the degradation rate by conserving part of the battery's capacity at the low end (the part of the battery when it chemically first begins to recharge), and the high end (that part of the battery that chemically recharges last). This is generally coupled with some sort of electronic indicator that tells the end user when the battery has reached "0% capacity," and "100% capacity." Each of these readings is not actually 0, and not actually 100, depending on the design. The difference is called the "buffer." So when the indicator reads 0, the actual remaining capacity may be 5, 10, 15%, etc., again depending on design. When the indicator reads 100%, the actual capacity may be 85, 90, 95%, etc. The electronic indicator is also associated with some sort of automatic cutoff - when the indicator reads 0%, the device will shut down and stop removing power from the battery. When the indicator reaches 100%, the battery will stop the chemical recharge process.

This does three things - it prevents the battery from actually completely discharging - true 0% - which will sometimes render a li-ion battery unrecoverable, and it prevents it from reaching its chemical capacity to recharge - true 100% - which will ultimately reduce the power it can deliver when fully charged - or degrade. It also allows the in-between capacity - or "usable" capacity - to "borrow" from the high and low end capacity over the life of the battery to mask the fact that the battery overall has lost capacity. In other words, even though the battery may have lost 5% of its ability to hold a maximum charge, the usable capacity is close to its original performance because it will use capacity from the buffer - up to a point.

That's why the battery in the iX can be warranted for 8 years, with less than a 30% reduction in capacity. And it's probably going to be a lot less, although we haven't reached the 8 year point in any if them. If you could fully use the buffer all of the time, that degradation would occur faster so nothing to be gained, and potentially more issues with charging and unrecoverable - expensive - batteries.

*To address the original question, you probably could charge to "100%" most - or all - of the time AC charging and not see a significant increase in capacity loss. It's just BMW being conservative (although leaving the battery at 100% state of charge increases the rate of reaction in the battery versus 80%, or 70%, or 60%, and an increased reaction rate means increased degradation, potentially significantly). OTOH, charging to 100% on a DC charger exposes the battery to more heat, potentially a lot more over a longer time, hence faster degradation, in addition to the increased charging time over about 80% (possibly double). Rather than explain in detail "this is when you should charge to 100%, this is when you shouldn't," BMW has just used a blanket, and safe, 80% "unless you need to" statement.

Do you know if either the bottom or top buffers are used in iX? I am pretty sure they are not in X5 PHEV.

[Paladin1]

I know that Mat Watson at CarWow and some other reviewers have run an iX beyond "0" and eked out another 10-20 miles, but I'm guessing that didn't deplete the buffer. Just a safety margin for owners. I doubt charging longer at 100% produces any more charge. You can run a li-ion battery to real zero - just run it until it stops and let it sit. Might take a few months, but eventually internal discharge will completely deplete the chemistry. In a home appliance with one or two cells that might mean the end of the battery - it can't be revived (unlike NiCad or NiMh batteries that can be "re-formed"). In a large EV battery some of the cells might be recoverable, but you definitely don't want to try it.

In a PHEV, the battery is so much smaller there isn't much of a buffer to begin with, so little impact.

[exxxviii]

Originally Posted by javapro

Do you know if either the bottom or top buffers are used in iX? I am pretty sure they are not in X5 PHEV.

Only BMW could say. I haven't even found a clear statement on the battery's actual size.

As Paladin1 noted, you can run the battery past 0%. Consumer Reports conducts their 70 MPH highway speed test in which they run the car until it stops and needs a flatbed. They reported that they got about 30 miles past when the car reported 0%. That would equate to 9% of extra phantom battery.

Nobody knows what the top threshold (or unused capacity is). Further, nobody knows if the BMS allows any of this to be used for any purpose. When the BMS reports 100%, it is possible that the actual state of charge is something below 100%. But, we do not know if the BMS prohibits regenerative braking when reporting 100% or if it allows use of that secret capacity above "100%."