Graph showing how charging rate deteriorates depending on battery charge level?

[daveo4EV]

keep in mind also all this charge rate management is _NOT_ based on physical limitations of the LiON battery cells - it's management by onboard software written by Porsche engineers who are "guessing" based on years of actual data as to how LiON cells "behave"…

the LiON cell doesn't give a crap if you charge it at full rate until 100% - but we factually know it won't last very long if we do that…

so we write software to control how each cell is receiving power - how much, how long, how fast, etc…

so when you are seeing a particular rate of charge - it is the software that is "choosing" that rate - why is it choosing that rate? Because Porsche has a warranty on the battery - and they are attempting to get you through the warranty period without them replacing the battery…and their software is in control of the entire process.

so all of this taper during fast charging, battery thermal limits so on and so forth - it's a giant SWAG (Scientific Wild Ass Guess) about best practices put into software to attempt to make the battery last long enough that you won't get a new battery from Porsche before the warranty is up.

A good friend, battery engineer for top tech company, CERN PhD theoretical physicist once told me at lunch:

You can actually do anything you want to LiON battery cell, any voltage, any temp, no taper, just charge or discharge at any rate at any time…if you don't care about charging that cell ever again…we manage all this because we want them to last more than a few charging cycles. But honestly the chemistry/physics don't limit the cell - the software limits the cell so that it will last longer.

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[Jrkennedy37]

all these charts are great and helpful planning tools

but there is an ideal taper curve (i.e. what can the Taycan do if everything goes "to plan") and then there is what actually happens during any particular charging session.

there are sooooooooooo many variables that you can never "plan" to achieve the optimal taper curve

as to what is happening during any particular charging session there is not enough information shown/displayed/available to properly diagnose as to why you are getting any particular charge rate for a given charging session

some (not all) of the variables that are invisible/out-side-your-control are:

• battery temp
• ambient temp
• battery age
• power grid limitations
• charging station hardware faults
• charging station software faults
• load reductions being imposed by the power company based on overall grid load
• shared load reduction due to other vehicles charging nearby
• lack of sufficient onsite power storage to boost charging rate (depletions of local "booster batteries" due to previous charging sessions)
• vehicle battery dynamics during the charging session - Taycan can reduce incoming load due to battery dynamics monitored during charging session
• EV battery thermal management efficiency
• charging station thermal management efficiency
• load reduction due to commerce based considerations (are you paying for the fastest rate)
• time of day
• anticipated load management - charging networks monitor historical usage patterns based on time-of-day/week and will sometimes reduce load to keep local storage batteries "full" for predicted/up-coming peak charging loads…
• etc…

basically there are many many many many reasons you may or may not achieve optimal charging rates when fast charging - as to why you are receiveing any particular charging rate for any given charging session you as the consumer do not have access to sufficient logs/data to determine where the system is constrained during any single session and why it's not charging faster

the _MOST_ common reasons for sub-optimal charging rates are:

• battery thermals out of "ideal" for fast charging
• ambient thermals out of "ideal" for fast charging
• local site-level problems/faults/restrictions on the fast charging station hardware (unpublished typically)

sometimes I've been charging at stall #4 getting a pathetic charging rate (60 kW or less) and simply moving from stall #4 to stall #2 restored my faith in humanity and increased my rate! why? I have no idea and with out full session logs (from both the station and vehicle) there is no way to tell - but factually that's true.

a good friend/track-buddy recently has taken the plunge into EV land - he has fast charged it a lot - and calls me for "advice" while on the road - he pulled into EA baker's field once with his eTron SUV and plugged into an EA station - he called me in "horror" at a 18 kW charge rate @ battery SOC of 5% and was agast/confused/mad/frustrated it was anticipating like 2 hour stop - he asked me "why?" - I said I don't know - he asked if there was anything he could do - I asked him if he'd tried changing stalls - he said no but all the other stalls were full - I then suggested it wouldn't hurt to change charging cables (EA stations have two cables) - he said ok - and stopped the session and swapped cables (not stalls) - plugged into the other cable - boom - 157 kW charge rate!!! (eTron SUV is a great EV with the 2nd best charge rate) - why was this true? We will never know…but factually that happend.

for me if I can get a sustained rate of 125 kW or more and get to about 85% or better - that's about as good as it gets these days given all the variables - and if you're getting 150 kW or more - basically that's golden and honestly the Taycan battery isn't big enough to spend much more than 25 min charging if you're getting 150 kW charge rate or more…and I have no problem killing 20 min during fast charging stop - it's when it stretches to 45 min or longer that I start to notice "hey this is taking a long time"…

YMMV - my $0.02

Sometimes a different cord/plug on the same stall fixes the speed. I had two stops with a bad cord pushing 5kw. Switching cords then gave me 265+kw. On the EA units there’s a telltale sound of a compressor that I’m guessing chills the coolant within the cord. The second time it happened, I didn’t hear that compressor kick on and knew right away speed would be limited.

 

[Tooney]

RE: different cords on EA charging stations.
I spoke to EA rep about the status on a particular charging station that MyPorsche app was reporting. The status on MyPorsche was the station was "occupied for 4+ hours, etc." (I was at home wanting to learn how to interpret MyPorsche's EA status info.)

She looked up her status on the station and said, that station is available, but one plug/cord is not working.​

I asked, so if you use the other plug, the station will charge?

She said, yes.​

I asked, if I drive up to this station, will I see that the station console shows there is a problem with one plug?

She said, no, the station console will show it is available for charging..​

I asked, how would I know that one plug is not working?

She said, you will get an error message after you plug in. But if you are able to use the other plug, it will work.​

She said if you sign up and use the EA charging app, it will show you the status of the individual plugs on each station.
I looked up the station on the EA app, and it showed one plug was not available, the other one was available.

 

[submatrix]

@daveo4EV what about the fact that Porsche reserves the top ~10% or so, thus only giving you ~90% of the battery usable anyway? Doesn't that mean that charging to "100%" in the Taycan is actually "not that bad" since Porsche will never actually fill all the cells up?

 

[Jrkennedy37]

RE: different cords on EA charging stations.
I spoke to EA rep about the status on a particular charging station that MyPorsche app was reporting. The status on MyPorsche was the station was "occupied for 4+ hours, etc." (I was at home wanting to learn how to interpret MyPorsche's EA status info.)

She looked up her status on the station and said, that station is available, but one plug/cord is not working.​

I asked, so if you use the other plug, the station will charge?

She said, yes.​

I asked, if I drive up to this station, will I see that the station console shows there is a problem with one plug?

She said, no, the station console will show it is available for charging..​

I asked, how would I know that one plug is not working?

She said, you will get an error message after you plug in. But if you are able to use the other plug, it will work.​

She said if you sign up and use the EA charging app, it will show you the status of the individual plugs on each station.
I looked up the station on the EA app, and it showed one plug was not available, the other one was available.

If you sign up for ABRP premium they source some of this info into the charger details. In the case of the throttled flow on the 350kw units I tried, those chargers showed operational in the app even though they were not functioning properly. It’s worth trying the opposite cord if your first try isn’t flowing quickly.

Here’s an example of a half broken charger in ABRP:

 

[daveo4EV]

@daveo4EV what about the fact that Porsche reserves the top ~10% or so, thus only giving you ~90% of the battery usable anyway? Doesn't that mean that charging to "100%" in the Taycan is actually "not that bad" since Porsche will never actually fill all the cells up?

yeah this is another variable we have no visibility to - again it's porsche's software that's holding back the charge rate at the 10% or so "reserve" capacity - the fact that it does factually taper while approaching "consumer-100%" mean's porsche's software is making this decision - and it's the same software that "knows" about the reserve - so Porsche's SWAG is to not push it…even though it's not technically 100% - although my guess/speculation is that there is more reserve on the bottom than the top - i.e. 100% is closer to physical/actual 100% vs. 0% - where there is probably a lot of capacity still left - but if you drive an LiON cell to actual zero% you brick it - where as it's simple "bad" to drive a LiON cell to actual 100% but you won't brick a battery…

again this is all magic undocumented and invisible buried inside the Porsche BMS (battery management software) and ever changing as we can witness with new charging behaviors with each software update - Porsche is basically guess here and rolling out policy changes via software updates as they learn more based on data from the field…

we simply don't know - and the only actual data we have is what we can deduce from observing the charge rate during a session - which is a bit like trying to count fish while looking at the surface of a lake…i.e. highly inaccurate the real data is beneath the surface.

 

[Jhenson29]

what about the fact that Porsche reserves the top ~10% or so, thus only giving you ~90% of the battery usable anyway?

Only 90% is usable, but that doesn’t mean the other 10% is at the top. Some is at the bottom. So, 100% user capacity isn’t 90% on the total. It’s higher. Maybe around 95% or so. And we don’t know how that may change over time either.

 

[submatrix]

Only 90% is usable, but that doesn’t mean the other 10% is at the top. Some is at the bottom. So, 100% user capacity isn’t 90% on the total. It’s higher. Maybe around 95% or so. And we don’t know how that may change over time either.

True, good point on it not necessarily being at the top.

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