SOH and reduced GOM reading

[JodyS21]

I do worry a bit about the battery (as my use case is that I need over 100 miles in winter & want the car to last us at least 5 years), but to be honest I'm not more worried now I've watched that video.
We all know this and that reduces/degrades the battery, there's not really much we can do about it realistically, we all need to use the car as our individual circumstances are; reduce max and min SOC if possible is probably the only thing one can realistically try to do.

Once I start seeing my SOH begin to reduce I will start worrying more though!

 

[Coulomb]

My understanding would be that state of charge is indeed the voltage and state of health the ability of the battery to deliver it’s full power.

Yes, the battery voltage correlates pretty well with state of charge (how full the battery is), at least for our battery chemistry.

The state of health is basically the percentage of energy that the battery can hold, compared to new. The figure is adjusted slightly so that at new, it's something like 103%, but anything over 100% is reported as 100%. That's presumably to prevent new owners from freaking out at the high initial degradation that is completely normal and unavoidable.

Calculating SOH is tricky, especially if the owner doesn't discharge the battery very much for a long period of time. So there are all sorts of heuristics, and there can be moderately large corrections from time to time as the battery management system gathers data. So it's not worth worrying about short term losses. Over about a year you can get some idea, but remember that the first year is expected to be worse than all others. A year is also good because you get all 4 seasons, and the seasons make a big difference to range and degradation rate.

The ability to deliver full power is a different thing. As batteries age, their internal resistance increases, and that reduces the ability to deliver full power. But I would not expect to detect that for many years. The problem of internal resistance is also worse with smaller batteries, e.g. the first generation Leafs and IMiEVs. Ours is a medium sized battery (though at the smaller end of the more recent EVs), so it should be less of an issue compared to the first generation EVs.

 

[Coulomb]

This may be a silly question. If the fully charged voltage remains the same how can the state of health be reducing?

Getting to the required battery voltage just means that the charge hasn't been aborted early due to poor balance. Usually this would happen if one or two cells are full before the others, so a full charge would over-charge those cells. Over-charging is very bad for cell life, so it's avoided at all costs.

So full battery voltage just means that the battery is full: it can't store any more energy. If the state of health is say 90%, that means that you only have 90% of the energy available when new, or a while after new. So the battery charge will deplete 11% faster (1/0.9 = 1.11) than when new. It will also charge 11% faster, since it only takes 90% of the time when new to fill the reduced capacity battery.

To use the bucket analogy: the volume of the bucket represents energy that can be stored in the battery. At 90% SOH, the top 10% (imagine a bucket with vertical sides) is cut off, so the bucket fills faster, but also runs out faster (for the same charge and discharge rates). The state of charge, and battery voltage, are scaled so that the top of the bucket, regardless of volume, is 100% and 450V (or whatever is full for your car). Obviously, with only 90% of volume in the bucket, the range is about 90% of new (or slightly less, since there are some small, fixed losses).

 

[mj224]

FWIW, my first EV was a little Citroen Zero. When I replaced it, its summer range was about 60 miles. The stated range was 93 miles. And the car was 10 years old, and almost always charged at home on its 3 pin charger...thus after 10 years the battery was down to 65% of its original capacity...

 

[MickH]

Getting to the required battery voltage just means that the charge hasn't been aborted early due to poor balance. Usually this would happen if one or two cells are full before the others, so a full charge would over-charge those cells. Over-charging is very bad for cell life, so it's avoided at all costs.

So full battery voltage just means that the battery is full: it can't store any more energy. If the state of health is say 90%, that means that you only have 90% of the energy available when new, or a while after new. So the battery charge will deplete 11% faster (1/0.9 = 1.11) than when new. It will also charge 11% faster, since it only takes 90% of the time when new to fill the reduced capacity battery.

To use the bucket analogy: the volume of the bucket represents energy that can be stored in the battery. At 90% SOH, the top 10% (imagine a bucket with vertical sides) is cut off, so the bucket fills faster, but also runs out faster (for the same charge and discharge rates). The state of charge, and battery voltage, are scaled so that the top of the bucket, regardless of volume, is 100% and 450V (or whatever is full for your car). Obviously, with only 90% of volume in the bucket, the range is about 90% of new (or slightly less, since there are some small, fixed losses).

Thank you for such an in depth reply.

 

[JodyS21]

Well I’ve just been surprised & shocked, I’d not looked at my SOH for a couple of weeks.
It’s now showing 99.22%
Odometer is on 9603 miles.
7 months old (to it being registered)

 

[Coulomb]

I’d not looked at my SOH for a couple of weeks.
It’s now showing 99.22%

Our SOH meters are probably all decreasing rapidly (since the batteries are fairly new), and this is being hidden from us for the first year or so.

My guess is that a lot of the earlier MGs in the UK will start to show some degradation soon. Your prize for being an early adopter, perhaps?

 

[Lovemyev]

Our SOH meters are probably all decreasing rapidly (since the batteries are fairly new), and this is being hidden from us for the first year or so.

My guess is that a lot of the earlier MGs in the UK will start to show some degradation soon. Your prize for being an early adopter, perhaps?

It’s inevitable really, if you charging / driving the car for what it was intended for :- “USE !”.
Then after a few years the HV battery will have degraded slightly.
It’s pure fact !.
More use, means more charges, means a slight decline in your actual range.
My car is now 18 months old and covered over 13,000 miles.
So yes, early adopter.
It is running on the latest software ( Jan 15th 2021 ).
The reported range on the GOM is pretty consistent in what it predicts of range after a full charge & balance.
Voltage on the pack is 448 - 449 volts and the predicted range on the GOM is anything around the 157 - 158 mile mark.
The car claims the pack is 100% fully charged each and every time of course.
But I am figuring that there is some degradation in the pack, which I think is to be expected, given the age and mileage covered.
Only given about 4 small “Splash and Dash” top up’s on rapid units.
99.9% of our charging is done at home on our 7.00 kw wall box.
I don’t have a device that is able to report my SOH - But my “Gut” tells me that there is a small amount of degradation.
I figure something like about 5 ish % ?.
I have no facts to back up this statement, but my instincts ( Gut Feeling” ) tell’s me so.
Am I concerned, no not really.
You have to expect some reduction in battery health at some point.
If your car is fairly new ( less than one year old and low mileage ) I would expect to see a predicted mileage range of around 163 miles.
This is on the new BMS software of course.
After 18 months and 13,000 miles it may not hit that magic 163 predicted range.
The car drives and performs just like it did when we first collected it.
The GOM is still doing a pretty good job of keeping pace with the actual mileage covered.
Just covered a 120 mile pleasure trip today, and the consumption figure is pretty good a 5.0 m/kWh.
Still a happy camper with regards to the car itself !.

 

[Johnnybee]

Hi There Lovemyev,
I am pleased to know that I'm not the only one. However I do like your consumption figures. At the moment I can only achieve 4m/kWh (Overall). I don't have a "Lead Foot" and use "E mode & Regen 1". As I'm new to EV's, am I driving the wrong way?. Any advice would be helpful to hone my driving skills.
Looking forward to tips of the Trade!!.

 

[Phil Hayward]

I got this consumption driving back from near the M4 towards Stroud on the A46. Air con on low setting. I tried to keep the power constant allowing it to slow up a bit on hills and speeding up going down hill.
Kers setting and drive mode will not make any difference, avoid drawing high current from the battery. I didn't go over 60 MPH and made an effort to drive smoothly to see how high I could get the KW per mile.I haven't tried hyper mileing, but I think someone got 6.5 Mpkw.
At an average speed of 70 MPH I was down to 3.4 on a twenty mile journey.
The MG is more fun if you can ignore the range estimate,

 

[Cocijo]

Hi There Lovemyev,
I am pleased to know that I'm not the only one. However I do like your consumption figures. At the moment I can only achieve 4m/kWh (Overall). I don't have a "Lead Foot" and use "E mode & Regen 1". As I'm new to EV's, am I driving the wrong way?. Any advice would be helpful to hone my driving skills.
Looking forward to tips of the Trade!!.

4mpk is not bad. I average around 4.2 during warmer Months and 3.2 in colder. The key factors are speed and driving style (heater in winter). I find the regen and econ settings make little difference. Stay below 20% power if you can and keeping below 60mph deliver best results. It’s easy to get excellent mpk on a shorter low speed trip but over a few thousand miles my average fairly consistently gets the above figures. I tend not to focus too much on economy unless I’m on a longer run and need the range.

 

[Johnnybee]

Thanks for the advice, I'm taking a 200m round trip this weekend ( none Motorway) it will be interesting to see what I can achieve.

 

[Kithmo]

I'm lucky to get 3.5 m/kWh with my, predominantly 3 mile there, 3 mile back trips every day, early morning.
I did get 4.5 m/kWh on a 90 mile each way trip to the coast last Summer, mostly A-roads with 50 mph limits.

 

[Lovemyev]

Hi There Lovemyev,
I am pleased to know that I'm not the only one. However I do like your consumption figures. At the moment I can only achieve 4m/kWh (Overall). I don't have a "Lead Foot" and use "E mode & Regen 1". As I'm new to EV's, am I driving the wrong way?. Any advice would be helpful to hone my driving skills.
Looking forward to tips of the Trade!!.

Hi @Johnnybee .
It's already been said and some great advice in the above posts.
Nothing more to add really, but I will add my two pennies worth as you did ask.
Achieving 5 + M/kwh's does require a few considerations and some practice to achieve on a more consistent basis.
If you want to maximise your range, you have to be a little careful with the "GO" pedal.
Imagine you have an egg trapped between the sole of your shoe and the "GO" pedal .
When pulling away from the lights or from a stand still, think about the "EGG" first !.
Oh ......... Just remember, it's NOT hard boiled .
Try and read the road ahead and use the regen in lieu of foot brake and try and reframe from the constant need to be "ON and Off" both of the pedals.
Personally, I only use the default mode of NORMAL and regen level 3.
Mastering the "GO" pedal over time plays a big part in the secret.
The car does not have full one pedal driving, but it's about as close as you can get.
Only using the foot brake, to bring the car to a complete stand still when stopping.
Apply the foot brake at the point when the car is at a very low MPH.
Using the HVAC can be a hungry beast and will devour your range quickly, just keep that in the back of your mind.
If you want to see the effect, then power up the car and observe the remaining range on the GOM.
Now, turn on the HVAC and increase the demand for heat to the cabin.
The higher the demand for heat or cooling, the more range will be reduced from your pack.
Expect to see a 15+ mile range reduction, straight away.
The fan / blower motor is not the cause, its the heater element inside the heater box that eats the power.
Of course their will be other factors outside that are totally outside of your control, like the weather traffic etc .
Travelling at 70mph ( and above ) will consume a lot more energy than driving at a more sedate speed.
The GOM on the ZS EV is pretty good in reporting the consumption of your remaining range.
Oh ......... I would also reset your trip meters before you set off as well !.
Bet your sorry you asked the question now !.

 

[Johnnybee]

Hi Lovemyev, Many thanks for your reply it was very enlightening!!. In a "Past Life" I have been a Driving Instructor, an Auto Mechanic and last but not least a HGV Driver. So I hope you would agree that my driving skills should be up to the mark, it's the regen settings I don't do well with. After driving MPV's and small SUV's for years my first EV was a Hyundai Ioniq, which was the Bee's Knee's to drive and regularly returned 5.5 - 6.5 m/KWh's. The downside however was after an hour or so of driving I couldn't walk with the amount of pain in my right hip. Hence the change to the MG. I appreciate the MG will never compete with the Ioniq, drag coefficient and all of that but at least in Ioniq the Regen could be switched off and one could coast whenever possible.
I guess I'll have to play about with the settings to see if I can improve things.

Once again, Many Thanks.

 

[Lovemyev]

Hi Lovemyev, Many thanks for your reply it was very enlightening!!. In a "Past Life" I have been a Driving Instructor, an Auto Mechanic and last but not least a HGV Driver. So I hope you would agree that my driving skills should be up to the mark, it's the regen settings I don't do well with. After driving MPV's and small SUV's for years my first EV was a Hyundai Ioniq, which was the Bee's Knee's to drive and regularly returned 5.5 - 6.5 m/KWh's. The downside however was after an hour or so of driving I couldn't walk with the amount of pain in my right hip. Hence the change to the MG. I appreciate the MG will never compete with the Ioniq, drag coefficient and all of that but at least in Ioniq the Regen could be switched off and one could coast whenever possible.
I guess I'll have to play about with the settings to see if I can improve things.

Once again, Many Thanks.

You are very welcome and given your extensive back ground, I would not attempt how to tell you how to suck egg’s my friend.
I just think you had a very efficient car to start with, that’s maybe where your problem lies !.
Save your energy, as the ZS is never going to match that type of efficiency.
You may get close under certain conditions if you REALLY tried hard.
Putting on your driving instructors cap may just help a little .
There are some more and less efficient EV’s out there, that’s is for sure !.
Some costing a LOT more than the ZS EV as well !.
I have never found any real advantage of switching the driving modes myself, to be totally honest.
I find it better to just stick with a mode you are happy with and then learnt to master it to your best advantage, with your right foot.
Normal mode suits my driving style just fine !.
There is no restriction on power if you really want it in an emergency situation, because flooring the “Go” pedal will automatically provide the same affect as selecting sports mode, without “Faffing” about with the mode selection switch.
Speaking from somebody who has moved from a low sporty five door hatchback, into the higher ride height of the ZS EV and with a knee replacement to deal with, the advantage’s of the higher ride height and less pain getting both in and out, should make the small loss of efficiency easier to deal with than your painful hip !.
Old age really sucks.
You do realise of course that your life in lower ride height cars is over now.
When I see a sporty car out on the road, then turn to my wife.
See always say’s the very same thing :-
“You can forget that, you might get in, but you will never get out”.
How right she is !.
Enjoy .

 

[Johnnybee]

Just caught you on the Bell Alerts, Yep getting old really really Sucks Big Time. I drove to Scunthorpe this morning to do some shopping and forgot to take my wallet.* DUH*

 

[Gomev]

Just caught you on the Bell Alerts, Yep getting old really really Sucks Big Time. I drove to Scunthorpe this morning to do some shopping and forgot to take my wallet.* DUH*

Did you forget about the local shops as well ?

 

[Lovemyev]

Just caught you on the Bell Alerts, Yep getting old really really Sucks Big Time. I drove to Scunthorpe this morning to do some shopping and forgot to take my wallet.* DUH*

Welcome to the club !.