Charging Best Practices

[Skilly]

Can you share what previously unannounced reserves Tesla tapped into any during Katrina (i.e. what exactly became abundantly clear)? AFAIK all they did it unlock software limited versions (S60/60D/70/70D) which was no secret - everyone who bought one knew exactly they had this untapped capacity and that it could be unlocked for a price. During Katrina, they just got this unlock for free for a limited time. Tesla did not tap into the anti-brick buffers - we know about those from the community reverse engineering efforts, such as the data from Jason Hughes you quoted earlier.

See the table above (earlier in the thread) highlighting all of the software restricted capacity. It's not limited to the 60/70 models. Although, as you noted, that was a commercial offering that could be upgraded for a fee.

I believe that during that period they also temporarily unlocked the reserves that they hold back for battery long term health across the fleet, which gave users access to the full value of the capacity.

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[madeyong]

Is there any way to see charging history from the Porsche Connect App? I’m using the PMCC and I can see limited history on the EVSE itself but I thought I read somewhere that it would communicate with the app and show charging stats. I can’t figure that out or find where I read it. For that matter, can you start or stop charging on the PMCC through the app? I guess you can by setting or changing the profile or timer but there’s no stop/start charge ability from the app? Just want to make sure I’m not missing anything. Thanks!

 

[kailifish]

I see. Maybe you are creating some secret downforce. It’s a new feature!

I see. Maybe you are creating some secret downforce. It’s a new feature!

*incoming* “ porsche spent millions and millions on RnD why would you go ahead and ruin it with this feature rah rah rah” ?

jokes aside, even with the electric port, i once didn’t close the small flap for fast charging, blocking the closing of the port. and almost drove off like that thinking it will close itself anyways.

 

[feye]

Is there any way to see charging history from the Porsche Connect App? I’m using the PMCC and I can see limited history on the EVSE itself but I thought I read somewhere that it would communicate with the app and show charging stats. I can’t figure that out or find where I read it. For that matter, can you start or stop charging on the PMCC through the app? I guess you can by setting or changing the profile or timer but there’s no stop/start charge ability from the app? Just want to make sure I’m not missing anything. Thanks!

The PMCC has a web interface you can connect to, via the built in WiFi. Need password came with the PMCC in a little envolop to get more info.

On the app there is consumption tab "since charging", for a charging history. That might help?

You could start the charging in the car with "direct charging" enabled and then use the app later to tick off "direct charging" to stop charging.

You can also activate timers/profiles in the app. I am not sure if that would start the charging. Never tried that...

 

[CAracer]

It does come with 8 year battery warranty. Why worry?

 

[CAracer]

Just curious how much labor is involved and cost to replace the batteries when they expire? Just wondering. Probably won't own the car for that long. I would think that the labor would be expensive?

 

[whitex]

I believe that during that period they also temporarily unlocked the reserves that they hold back for battery long term health across the fleet, which gave users access to the full value of the capacity.

I don't think that is true, for a number of reasons. I've been a part of the Tesla community, including the hacking community, and all I've ever read was that during Katrina Tesla only unlocked the top end unused capacity which was unlockable for a price anyways. More importantly, Tesla batteries die completely if ever discharged to true 0% (used to happen to Roadsters, hence the anti-brick buffer for Model S and later). Batteries actually go into deep hibernation mode when operating in the anti-brick buffer range, to preserve themselves. While in that mode, they shut off battery heat/cooling, the battery will not turn on, and can only be trickle charged back out of the anti-brick region. There is no way Tesla would have risked damaging people's batteries by allowing them to discharge the battery to true 0, or even close. Battery replacement back then was over $40K each, so a high cost to Tesla, but I would also think running out of charge and a tow to nearest supercharger (or even a "tow charge") is much better if you're evacuating somewhere than bricking your car completely, not recoverable without a battery swap.

 

[Fish Fingers]

Just curious how much labor is involved and cost to replace the batteries when they expire? Just wondering. Probably won't own the car for that long. I would think that the labor would be expensive?

The battery price is very reasonable ??

Small battery.....
https://parts.byersporsche.com/p/Po...Motor-Battery-Pack/103052090/9J1915100AM.html

 

[madeyong]

The PMCC has a web interface you can connect to, via the built in WiFi. Need password came with the PMCC in a little envolop to get more info.

On the app there is consumption tab "since charging", for a charging history. That might help?

You could start the charging in the car with "direct charging" enabled and then use the app later to tick off "direct charging" to stop charging.

You can also activate timers/profiles in the app. I am not sure if that would start the charging. Never tried that...

Thanks very much. I also figured out that if you log into My Porsche and select the “Charging at Home” service you can see the PMCC connected to your My Porsche account and display the charging history (including the length of charges and total kWh delivered). You can even generate a PDF report by date range.

I purchased a CPO 2020 TTS from an out of state Porsche dealer. While the PMCC came in the bag in the trunk with all of the manuals and attachments, it doesn’t seem to have the little envelope with the password for the web interface. I really don’t need it given the My Porsche method and others you mentioned but just wondering if there is a way to reset the password?

 

[Skilly]

More importantly, Tesla batteries die completely if ever discharged to true 0% (used to happen to Roadsters, hence the anti-brick buffer for Model S and later).

Maybe Roadsters as that was really their customer lead beta program. That was my point though - Ive had both a P85D and P100D and I can tell you that I had both vehicles twice to 0% and they continued on for several miles to a safe charge location. There are also a couple of documented cases of the same on the Tesla forum.

Tesla is horrible at explaining updates in their release notes and plays with battery management and other key elements of the cars operation in the releases. So, it might no longer be the case. But I can tell you with personal experience that I ran to 0% on more than one occasion....the first time in particular I recall because it was my wife running close to home and I was watching her progress and the battery levels on the app (with fingers crossed).

Regardless, the point is being missed. The buffer IS my question and about what is actually 80% (or zero percent for that matter) since that measurement is not a true reflection of what is actually in the battery.

 

[Squiden]

More frequent shallow charges are better than less frequent deep charges.

You have an 8 year warranty. If you have an EVSE in your garage, stop overthinking it and plug in nightly so you have the range if needed. There is no proven reason to wait till any % SOC.

I charge to 80% daily, whether the car is at 50% or 75%.

Do you have any data supporting this? One could argue that it is more beneficial to charge deeper once as the batteries need to warm up to an optimal charging temperature, so many shallow charges ends up in charging at not optimal charging temperature. I'm curious as to the source of your information.

I work on satellites that use Li-Ion batteries and agree with Smohr33. In orbit, we can see tens of cycles a day going in-and-out of eclipse, so maintaining battery health is a critical function since we want these to last for many years in-orbit. While there is numerous different cell chemistries that are used by cell manufacturers, I expect most Li-ion cells to behave similarly from a life standpoint.

While I can't share the actual test report since it's proprietary to the cell vendor, I can share some findings from some of their life testing going through 5000 discharge cycles under various conditions (charge/discharge rate, temperature, depth of discharge):

- Heavy discharge / charge cycles ((C)apicity/2 rates, which would only be ~58 Amps for us - 93kWh battery/800V = ~116Ahr) from 100% to 0% and back caused the biggest degradation - the batteries only lasted <1000 cycles before falling below 80%. While we physically can't discharge at C/2 for more than a few seconds, some of us are likely charging at rates greater than C/5 (23A) regularly.

- Heavy discharge / charge cycles (C/2) from 100% to 60% resulted in a ~10% degradation after 2500 cycles.

- Mild discharge / charge cycles (C/5) from 100% to 60% resulted in only a ~8-9% degradation after 2500 cycles.

- Mild discharge / charge cycles (C/5) from 100% to 80% resulted in only a ~5% degradation after 2500 cycles.

- Mild discharge / charge cycles (C/5) from 100% to 90% resulted in only a 2% degradation after 5000 cycles (yes, double the cycles than the other tests performed, with less degradation).

For the space rated batteries, temperature doesn't look to play a big role on degradation, but does impact how fast we can charge/discharge the batteries, so we tend to keep them cold when not in use (0 degC when battery is fully charged), and 20 degC when charging/discharging (we pre-heat before the eclipse, then the draw on the battery tends to be able to keep it at that temp). During long periods of no battery usage (out of eclipse season), we tend to drop the batteries down <80% capacity for storage.

So, what does that all mean? How frequently you charge actually has little effect on battery life - it's really how much battery you 'use'. You basically get the same degradation for the same amount of battery used - 2500 cycles at 20% versus 5000 cycles at 10% end up causing a 4-5% degradation of the total battery capacity (so equal energy used in those 2 cases). And 2500 cycles at the 40% DoD caused 8-10% degradation of the total battery - also in-line. Thus, the biggest limitation on Li-Ion batteries is big discharges (>80%), and heavy charge/discharge cycles (C/2). I know I've seen other test reports that show data for C and 2C discharge rates as well, but I'm not finding them at the moment.

I believe this is all consistent with what EV owners have seen - you don't want to use the fast chargers everywhere, and avoid deep discharges on the battery (<20%). You can potentially extend the life a little bit by charging at even slower rates - I actually backed my home charger off to 20A because I have no savings having it take 8 hours versus 4 hours over night (and I was occasionally getting overtemp warnings on the charging unit on the hot summer days).

(Edit - fixed math on the conversion of kWh to Ah)

 

[madeyong]

Great info! Thanks!!

 

[jcroix]

I work on satellites that use Li-Ion batteries and agree with Smohr33. In orbit, we can see tens of cycles a day going in-and-out of eclipse, so maintaining battery health is a critical function since we want these to last for many years in-orbit. While there is numerous different cell chemistries that are used by cell manufacturers, I expect most Li-ion cells to behave similarly from a life standpoint.

While I can't share the actual test report since it's proprietary to the cell vendor, I can share some findings from some of their life testing going through 5000 discharge cycles under various conditions (charge/discharge rate, temperature, depth of discharge):

- Heavy discharge / charge cycles ((C)apicity/2 rates, which would only be ~58 Amps for us - 93kWh battery/800V = ~116Ahr) from 100% to 0% and back caused the biggest degradation - the batteries only lasted <1000 cycles before falling below 80%. While we physically can't discharge at C/2 for more than a few seconds, some of us are likely charging at rates greater than C/5 (23A) regularly.

- Heavy discharge / charge cycles (C/2) from 100% to 60% resulted in a ~10% degradation after 2500 cycles.

- Mild discharge / charge cycles (C/5) from 100% to 60% resulted in only a ~8-9% degradation after 2500 cycles.

- Mild discharge / charge cycles (C/5) from 100% to 80% resulted in only a ~5% degradation after 2500 cycles.

- Mild discharge / charge cycles (C/5) from 100% to 90% resulted in only a 2% degradation after 5000 cycles (yes, double the cycles than the other tests performed, with less degradation).

For the space rated batteries, temperature doesn't look to play a big role on degradation, but does impact how fast we can charge/discharge the batteries, so we tend to keep them cold when not in use (0 degC when battery is fully charged), and 20 degC when charging/discharging (we pre-heat before the eclipse, then the draw on the battery tends to be able to keep it at that temp). During long periods of no battery usage (out of eclipse season), we tend to drop the batteries down <80% capacity for storage.

So, what does that all mean? How frequently you charge actually has little effect on battery life - it's really how much battery you 'use'. You basically get the same degradation for the same amount of battery used - 2500 cycles at 20% versus 5000 cycles at 10% end up causing a 4-5% degradation of the total battery capacity (so equal energy used in those 2 cases). And 2500 cycles at the 40% DoD caused 8-10% degradation of the total battery - also in-line. Thus, the biggest limitation on Li-Ion batteries is big discharges (>80%), and heavy charge/discharge cycles (C/2). I know I've seen other test reports that show data for C and 2C discharge rates as well, but I'm not finding them at the moment.

I believe this is all consistent with what EV owners have seen - you don't want to use the fast chargers everywhere, and avoid deep discharges on the battery (<20%). You can potentially extend the life a little bit by charging at even slower rates - I actually backed my home charger off to 20A because I have no savings having it take 8 hours versus 4 hours over night (and I was occasionally getting overtemp warnings on the charging unit on the hot summer days).

(Edit - fixed math on the conversion of kWh to Ah)

Let me say that I’m not disputing your numbers. I’m trying to better understand your numbers with respect to home charging. I really appreciated the in-depth post, so please correct me if I missed something.

First, are the numbers you provided numbers that were measured directly at the battery terminals? For example, when we plug a PMCC into a 40 amp/240V line, we’re actually going to use 32 amps continuous charging, or 7.7kW at the input to the PMCC. I don’t have my Taycan yet (it’s at the Houston port as I write this), but I’ve seen videos that show the Taycan reporting actual power it “sees”, which is always less than what the charger says it’s getting as input. I don’t know where along the electrical path between input port and battery that Porsche measures, but there’s obviously loss of power going to the battery. It could be that some is siphoned off for other functions, there’s the AC/DC converter loss, etc. The point is, 32 amps @ 240V in is not 32 amps @ 240 V at the battery.

Second, the Porsche battery is 800V, not 240V, as you pointed out. So 7.7kW at the battery (let’s assume no loss for a second), is only 9.6 amps into the battery after the 240V AC to 800V DC conversion. Even if I had a much larger charger, odds are that I’m not going to hit the C/5 number you prescribe (18.6kW charging = 23.25 amps @ 800V). A 19.2kW charger looks like it exceeds C/5, but when you reduce the power to what actually hits the battery due to loss between input port and battery, you’re probably down to the 18.6kW number, or close. So even a 100 amp line @ 240V is probably safe with the C/5 limit (80 amp continuous * 240V = 19.2kW).

So unless I missed something, I believe one big point to take away from your post is that you’re probably safe with any AC charging scenario for the Taycan. Charging at higher than 19.2kW (i.e. DC chargers) will degrade your battery faster, which aligns exactly with what Porsche advocates. Even people that paid for the 19.2kW charging option (I didn’t) should be safe if they can find a way to charge at that rate.

The other important point I got from your post is to keep the battery above 20% charge if possible. This, too, seems to align with Porsche’s recommendation. They advise no more than 80% charge on the top side and, by symmetry, I’d guess no less than 20% on the bottom side (still reading the user manual, so haven’t seen a recommendation on the lower side yet).

Would you concur?

 

[Squiden]

Let me say that I’m not disputing your numbers. I’m trying to better understand your numbers with respect to home charging. I really appreciated the in-depth post, so please correct me if I missed something.

First, are the numbers you provided numbers that were measured directly at the battery terminals? For example, when we plug a PMCC into a 40 amp/240V line, we’re actually going to use 32 amps continuous charging, or 7.7kW at the input to the PMCC. I don’t have my Taycan yet (it’s at the Houston port as I write this), but I’ve seen videos that show the Taycan reporting actual power it “sees”, which is always less than what the charger says it’s getting as input. I don’t know where along the electrical path between input port and battery that Porsche measures, but there’s obviously loss of power going to the battery. It could be that some is siphoned off for other functions, there’s the AC/DC converter loss, etc. The point is, 32 amps @ 240V in is not 32 amps @ 240 V at the battery.

Second, the Porsche battery is 800V, not 240V, as you pointed out. So 7.7kW at the battery (let’s assume no loss for a second), is only 9.6 amps into the battery after the 240V AC to 800V DC conversion. Even if I had a much larger charger, odds are that I’m not going to hit the C/5 number you prescribe (18.6kW charging = 23.25 amps @ 800V). A 19.2kW charger looks like it exceeds C/5, but when you reduce the power to what actually hits the battery due to loss between input port and battery, you’re probably down to the 18.6kW number, or close. So even a 100 amp line @ 240V is probably safe with the C/5 limit (80 amp continuous * 240V = 19.2kW).

So unless I missed something, I believe one big point to take away from your post is that you’re probably safe with any AC charging scenario for the Taycan. Charging at higher than 19.2kW (i.e. DC chargers) will degrade your battery faster, which aligns exactly with what Porsche advocates. Even people that paid for the 19.2kW charging option (I didn’t) should be safe if they can find a way to charge at that rate.

The other important point I got from your post is to keep the battery above 20% charge if possible. This, too, seems to align with Porsche’s recommendation. They advise no more than 80% charge on the top side and, by symmetry, I’d guess no less than 20% on the bottom side (still reading the user manual, so haven’t seen a recommendation on the lower side yet).

Would you concur?

Excellent point on the 240V versus 800V - you are correct - I was crossing the input versus output sides! I think all your math adds up - thanks for the correction!

 

[Fish Fingers]

Great info! Thanks!!

Totally agree!

It's what I love about this forum, compared to all other car forums I have been on.

The quality and input from most members is exceptional. There are a lot of smart people on this forum.
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