Running the Battery to 0%

[Box Cat]

I think it’s perfectly fine to drive the battery down occasionally if needed. You wouldn’t want to do it on a regular basis for longer battery life, but this chemistry will last for a long time.

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[MaintGrl]

Only a small population got those, when my truck came in August 2022 I didn't get one.

Nor I, mine was purchased Dec. of 23

 

[Maquis]

I think it’s perfectly fine to drive the battery down occasionally if needed. You wouldn’t want to do it on a regular basis for longer battery life, but this chemistry will last for a long time.

You need to re-read post 30.

 

[Gimme_my_MME]

Based on what I've seen in testing this cell, I'm going to make sure I do not go below 20% of actual SOC

Are you testing cell alone or pack with OEM algorithms?

 

[djwildstar]

The best possible explanation given is that maybe the BMS calibration gets out of sync over time, but that in itself is a bit concerning. This truck simply can’t be trusted on a regular basis at low SOC, and I don’t have an explanation as to why and neither does Ford at this time.

My advice is to avoid running her below 5% if you don’t absolutely need to.

Good advice!

I think that there are two things going on here:

First, like practically all EVs, the Lightning uses an integration method ("coulomb counting") as the primary way to estimate state of charge. Basically, the truck's computers measure power into the battery during charging and power out of the battery during driving to estimate how much charge is left. This method is the equivalent of dead-reckoning navigation, so it can have problems with rounding errors, long-term drift, and battery degradation, etc. Most EVs (I believe including the Lightning) "reset" the counters when the battery is at a known state of charge, but it still isn't unusual for the state-of-charge estimation to be a few percent off.

Second, and unlike most other EVs, Ford's EVs do not have any official "reserve" below 0% state of charge. Like all other EV-makers, Ford doesn't let you use all of the battery capacity. Like most other EVs, about 5% to 10% of the battery pack is "off-limits", mostly to protect the battery from excessive degradation.

For example, an ER Lightning has a 143.3kWh battery, but the software limits you to using only 131kWh of this capacity (91%). A 2018 Tesla Model 3 Mid-Range had an 80kWh battery pack and allowed you to use 74kWh of this capacity (93%).

In the case of Ford vehicles, the extra capacity is at the "top", meaning that the battery is never actually fully charged, but can be fully discharged. Many other EVs reserve at least a little bit of capacity at the "bottom" of the battery, so that the battery is never actually fully charged and never actually fully discharged.

To go back to our example, in an ER Lightning when you've got a 100% state of charge on the display, you have 131kWh of charge in a 143.3kWh battery, for a 91% actual state of charge. When you've got 0kWh of charge in a 143.3kWh battery, for a 0% actual state of charge.

Tesla reportedly uses 4kWh reserve at the "bottom" of the battery. So in our example at an indicated 0% charge, the pack actually has 4kWh in it, for a 5% actual state of charge; at 100% indicated charge, the pack actually has a 78kWh charge, for a 97.5% actual state of charge.

This also explains why Tesla recommends 80% daily charging while Ford recommends 90%. At 80% indicated charge, the Tesla battery is at a 79% actual state of charge, while at a 90% indicated charge, the Ford battery is at an 82% actual state of charge.

Having few kWh in reserve below 0% indicated state of charge allows for a more consistent driving experience all the way down to empty. This is because errors in estimating battery charge are unlikely to be larger than the reserve. The Ford approach probably better-protects the battery in cases where it is charged to 100% on a regular basis -- I'm guessing Ford doesn't want to have to replace batteries under warranty, and also doesn't want the bad press that would result from denying warranty claims because the customer "charged to 100% too often". The drawback is that you can run out of energy with relatively little warning any time you are under about 5% state of charge.

 

[Grumpy2]

Based on what I've seen in testing this cell, I'm going to make sure I do not go below 20% of actual SOC

Are you going to be able to share a little about what you now know about these cells? I hope so....

 

[Yellow Buddy]

Based on what I've seen in testing this cell, I'm going to make sure I do not go below 20% of actual SOC

Did you decide to sell yours yet? Mine goes on the market the same day yours does.

You’re my canary.

 

[Nklem]

By September of 2022 I don't think these were added to the vehicles. I didn't have one in mine.

I looked at a 9/23 build that came with one loose in the frunk....

 

[Box Cat]

You need to re-read post 30.

That is after reading post 30…
You can definitely choose to never run lower than 20% but occasionally going down to 0% won’t affect much longevity (same as going to 100% real capacity). That is what I do with battery packs I build. The BMS (set properly) will make sure you do not irreversibly damage the cells in the packs. The main reason why you have 140kwh and only use 130 is that with time those 140 will shrink to 130 and the truck will maintain its range so to speak, for say 10 years or as long it gets depending on usage.

 

[Maquis]

That is after reading post 30…
You can definitely choose to never run lower than 20% but occasionally going down to 0% won’t affect much longevity (same as going to 100% real capacity). That is what I do with battery packs I build. The BMS (set properly) will make sure you do not irreversibly damage the cells in the packs. The main reason why you have 140kwh and only use 130 is that with time those 140 will shrink to 130 and the truck will maintain its range so to speak, for say 10 years or as long it gets depending on usage.

But he’s testing the cells actually used in our truck.

 

[MickeyAO]

Did you decide to sell yours yet? Mine goes on the market the same day yours does.

You’re my canary.

Not selling...just don't like the HPPC (Google it if you want) test below 20% SOC We test the cell directly at actual cell capacity (Vmax to Vmin static capacity before HPPC test).

Even worse above or below 25C.

We have finished characterization testing and are moving into calendar and cycle life testing. Pilot run starts by Friday

 

[Box Cat]

These cells have a known chemistry and unless defective have known properties.

I disagree with the conclusion of not using the battery below 20% in any conditions unless I am misunderstanding what has been said.

You can just as easily monitor your packs through the obd port. There are a number of useful stats from the BMS, not only SOH, but cells balance etc.

For longevity and use compromise, running between 20% and say 80% on a regular basis is better than constantly go 100 to close to 0, that is for sure. But you can fully use the whole range if you need, just like the manufacturer suggests. From a practical perspective most people don’t drain their battery/tank anyway.

The point is you can go close to 0% if you need and that will not damage the cells (whatever the real or effective SoC the number actually refers to).

The BMS will stop the whole pack before the weakest cell goes below a spec, given a lot of factors.

But if you do it on a regular basis you will decrease the state of health more rapidly.

Just my humble opinion my friend

 

[MickeyAO]

These cells have a known chemistry and unless defective have known properties.

I disagree with the conclusion of not using the battery below 20% in any conditions unless I am misunderstanding what has been said.

You can just as easily monitor your packs through the obd port. There are a number of useful stats from the BMS, not only SOH, but cells balance etc.

For longevity and use compromise, running between 20% and say 80% on a regular basis is better than constantly go 100 to close to 0, that is for sure. But you can fully use the whole range if you need, just like the manufacturer suggests. From a practical perspective most people don’t drain their battery/tank anyway.

The point is you can go close to 0% if you need and that will not damage the cells (whatever the real or effective SoC the number actually refers to).

The BMS will stop the whole pack before the weakest cell goes below a spec, given a lot of factors.

But if you do it on a regular basis you will decrease the state of health more rapidly.

Just my humble opinion my friend

You might want to review some of my previous posts about observations from actual lab testing at the cell level. What the BMS and modules do? I don't care. But I know after 12 years of cell testing what the cells are doing (and currently testing the SK One E805A from an actual F150 Lightning that we dismantled after vehicle testing)

If you are monitoring your pack, you might want to find the PID for cell, module, or pack resistance to see my new concern.

Can you take it down to 0% rated? YES! Will I take mine below 20% SOC Actual? No.

Don't care to take what I say into account? You do you Boo! I just try to give hints about what I see in controlled cell level testing.

Please don't read any disrespect or attack against you into this post.

 

[MickeyAO]

You might want to review some of my previous posts about observations from actual lab testing at the cell level. What the BMS and modules do? I don't care. But I know after 12 years of cell testing what the cells are doing (and currently testing the SK One E805A from an actual F150 Lightning that we dismantled after vehicle testing)

If you are monitoring your pack, you might want to find the PID for cell, module, or pack resistance to see my new concern.

Can you take it down to 0% rated? YES! Will I take mine below 20% SOC Actual? No.

Don't care to take what I say into account? You do you Boo! I just try to give hints about what I see in controlled cell level testing.

Please don't read any disrespect or attack against you into this post.

I should also mention the resistance problem MAY NOT be real, but an artifact from what we had to do to the tabs in order to under go testing, but I'm not a big believer in that hypothesis right now.

 

[Yellow Buddy]

You might want to review some of my previous posts about observations from actual lab testing at the cell level. What the BMS and modules do? I don't care. But I know after 12 years of cell testing what the cells are doing (and currently testing the SK One E805A from an actual F150 Lightning that we dismantled after vehicle testing)

If you are monitoring your pack, you might want to find the PID for cell, module, or pack resistance to see my new concern.

Can you take it down to 0% rated? YES! Will I take mine below 20% SOC Actual? No.

Don't care to take what I say into account? You do you Boo! I just try to give hints about what I see in controlled cell level testing.

Please don't read any disrespect or attack against you into this post.

At this point I’ve run my pack multiple times 100-5% (and below) and several times to 0% and will likely do so given that some stretches I drive just barely makes it with the available range for that leg.

I figure with the depreciation it becomes my primary home backup that can do Home Depot runs in a severe degradation situation…but based on what you’re seeing, how bad will it be?

Or is it just that below 20% the data is simply not all too reliable given the variations of the HPPC?

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