What is your SOH? Milage? and how do you use your Battery?

[Zprime29]

I hear heat is the enemy. I had a sudden drop after a hot day when the truck was under the sun followed by a short fast charging session (dropped to 98.5% when I was under 10K). It went down to 98% later and came backup to 98.5% where I am now at 16K and 26 months. I didn’t plug in the truck in last two winters. Not sure how much damage cold does.

People say it drops faster at first and then slows down but even if you go down linearly, you will be at 91% SOH at 100K. Not too bad.

SOH is not a useful metric in my opinion, since we don't know how its computed. Linear degradation would mean 94% of capacity at 100k. That to me, is a much more tangible metric.

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[Maxx]

SOH is not a useful metric in my opinion, since we don't know how its computed. Linear degradation would mean 94% of capacity at 100k. That to me, is a much more tangible metric.

That number definitely sounds better. It would be cool to know how they calculate SOH. If they just make a guess based on the number of months, how often battery has gone over and under a certain temp, how often it has gone through high current change and discharge over certain temps, .... or they actually have a way to measure internal resistance of the cells.

Keep in mind the energy presented to ODB-II by BMS is just as much of a guesswork as SOH if not more. My guess is energy is calculated using parameters like SOC (which has been inconsistent and unreliable). Historical data (which can be reset). Current battery temperature and most likely SOH itself as well; since energy has to account for available capacity. So if SOH is unreliable, any calculation using energy is bound to be as unreliable or even more unreliable.

Of course as you mentioned, I don't know any of this for a fact. Anything we read from ODB-II is what Ford is telling us and much of it is calculated not direct measurment. It is all a mater of faith and we can all chose our GODs with little to no proof.

 

[Zprime29]

That number definitely sounds better. It would be cool to know how they calculate SOH. If they just make a guess based on the number of months, how often battery has gone over and under a certain temp, how often it has gone through high current change and discharge over certain temps, .... or they actually have a way to measure internal resistance of the cells.

Keep in mind the energy presented to ODB-II by BMS is just as much of a guesswork as SOH if not more. My guess is energy is calculated using parameters like SOC (which has been inconsistent and unreliable). Historical data (which can be reset). Current battery temperature and most likely SOH itself as well; since energy has to account for available capacity. So if SOH is unreliable, any calculation using energy is bound to be as unreliable or even more unreliable.

Of course as you mentioned, I don't know any of this for a fact. Anything we read from ODB-II is what Ford is telling us and much of it is calculated not direct measurment. It is all a mater of faith and we can all chose our GODs with little to no proof.

I think that's backwards. SoC is based on a combination of voltage and energy spent.

I charged to 100%, giving the BMS a known reference point. Then drove until I hit 14% without charging. I then charged it back to 100%. This gives the BMS a very good estimate of the energy in the pack via coulomb counting. The total energy, I believe is the reference value for determining what % our SoC is.

Maybe @MickeyAO can set us straight on the general concept between SoC and SOH.

 

[Maxx]

I think that's backwards. SoC is based on a combination of voltage and energy spent.

I charged to 100%, giving the BMS a known reference point. Then drove until I hit 14% without charging. I then charged it back to 100%. This gives the BMS a very good estimate of the energy in the pack via coulomb counting. The total energy, I believe is the reference value for determining what % our SoC is.

Maybe @MickeyAO can set us straight on the general concept between SoC and SOH.

On second thought what you are saying about Energy makes sense.

 

[Firn]

I dont believe SOC is based upon capacity. We see a wide variation in calculated capacity for any given temp, if soc was based on capacity we would see less than 100% soc for cold batteries.

I believe that soc is just voltage as I see ~4.09v per cell at 100% soc regardless of temp.

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In other news.

Having just had my high voltage contactor replaced i did notice a change in capacity, previously 100% was a capacity of around 126kwh, now it topped out at 131.07. What was interesting was that it continued to take in a lot of energy even after reaching 131.07, but the capacity didn't change.

 

[Maxx]

I think that's backwards. SoC is based on a combination of voltage and energy spent.

I charged to 100%, giving the BMS a known reference point. Then drove until I hit 14% without charging. I then charged it back to 100%. This gives the BMS a very good estimate of the energy in the pack via coulomb counting. The total energy, I believe is the reference value for determining what % our SoC is.

Maybe @MickeyAO can set us straight on the general concept between SoC and SOH.

I gave this some more thought to see where any inaccuracy could come from. P = V x I . As you go from 100% SOC to 14% SOC Voltage changes continuously but somewhat linearly. However current changes differently every time you accelerate or decelerate. And small errors can add up over the span of 86% SOC reduction.

I was also thinking about possible ways they are figuring out the SOH. R = V/I. They probably do this at the factory for SP and EP batteries when new and have it in BMS as a constant. Every time you charge to 100% (Or may be another SOC) they look at the current for that voltage when you move to calculate the internal resistance of the battery and compare to original resistance. Or may be they simply measure the voltage at 100% and compare?

Of course I am pulling all of this out of my......hat.

 

[Zprime29]

I gave this some more thought to see where any inaccuracy could come from. P = V x I . As you go from 100% SOC to 14% SOC Voltage changes continuously but somewhat linearly. However current changes differently every time you accelerate or decelerate. And small errors can add up over the span of 86% SOC reduction.

I was also thinking about possible ways they are figuring out the SOH. R = V/I. They probably do this at the factory for SP and EP batteries when new and have it in BMS as a constant. Every time you charge to 100% (Or may be another SOC) they look at the current for that voltage when you move to calculate the internal resistance of the battery and compare to original resistance. Or may be they simply measure the voltage at 100% and compare?

Of course I am pulling all of this out of my......hat.

You bring up a good point about current not being a one way street on that test. I forgot about the energy gain from regen braking.

I wish we knew just how to interpret SOH, let alone how it's computed. Is it how they determine the useful life remaining in the battery? Since time is also a factor in degradation, I suspect it also plays a role in the formula.

Let's take a hypothetical: Assume the SOH says 85% but the battery still shows 92% of the original capacity. How do you interpret that? The lower SOH implies (I'm speculating here) that the battery has seen lots of situations that are believed to degrade capacity. The higher actual capacity implies a factor in the SOH isn't being computed accurately. Perhaps it is old, but hasn't been driven to very low SOC and in mild weather.

On the flip side, what if the SOH shows 95% but the actual capacity is at 85%? Young battery, mild weather, but driven to under 10% and DCFC every day? I've seen reports of Tesla's being used for ride share that still hold good battery capacity, but they never report it's SOH ( I'm sure Tesla computes it differently, but would still be a good data point).

 

[Maxx]

You bring up a good point about current not being a one way street on that test. I forgot about the energy gain from regen braking.

I wish we knew just how to interpret SOH, let alone how it's computed. Is it how they determine the useful life remaining in the battery? Since time is also a factor in degradation, I suspect it also plays a role in the formula.

Let's take a hypothetical: Assume the SOH says 85% but the battery still shows 92% of the original capacity. How do you interpret that? The lower SOH implies (I'm speculating here) that the battery has seen lots of situations that are believed to degrade capacity. The higher actual capacity implies a factor in the SOH isn't being computed accurately. Perhaps it is old, but hasn't been driven to very low SOC and in mild weather.

On the flip side, what if the SOH shows 95% but the actual capacity is at 85%? Young battery, mild weather, but driven to under 10% and DCFC every day? I've seen reports of Tesla's being used for ride share that still hold good battery capacity, but they never report it's SOH ( I'm sure Tesla computes it differently, but would still be a good data point).

Not sure about relationship between SOH and capacity. However if I was designing the interface, I would use the estimated/actual battery capacity in displayed SOC. In other words if the battery has lost 15% of its capacity, SOC should never go above 85%. The fact that company warranty covers the battery bellow 70% but capacity is not shown anywhere on the interface was probably decided by their lawyers, not their engineers.

 

[Zprime29]

Not sure about relationship between SOH and capacity. However if I was designing the interface, I would use the estimated/actual battery capacity in displayed SOC. In other words if the battery has lost 15% of its capacity, SOC should never go above 85%. The fact that company warranty covers the battery bellow 70% but capacity is not shown anywhere on the interface was probably decided by their lawyers, not their engineers.

And we thought people complained a lot because estimated range wasn't showing spec. Can you imagine the flood of people complaining that they can't charge to 100%?

Seriously though, I agree. There should be a screen somewhere that shows us the "warranty %" for the battery. I might ask my service to check it just for fun (assuming they know how) when I take it in for my 40k in a month. Perhaps we could glean some info by comparing it to what CarScanner reports.

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