Daily Charging Limit Percentage - what's yours set to?

[Calvin H-C]

Many threads on this. There will be 16 responses with 21 answers, most of them worthless opinions...

Just speculation for the most part, partly from something one may have read somewhere sometime.

Here's a bit more speculation on my part, but based on eight years and 176,000+ km of experience with a Ford Focus Electric...

Charging to 100%: with the FFE, that's one's only option, unless you manually unplug, or if charging is incomplete when the "value charging" window ends.

Given the average range in a full charge (160 km), the mileage on the vehicle, and the fact that the average charge would start at about 50%, that means my battery has likely endured at least 2500 charging cycles to 100%. I'm still getting pretty much the same range as when the car was new, so it doesn't appear charging to 100% is doing anything detrimental.

When one charges to 100%, the battery control module will perform cell balancing at the end. I suspect this is likely good for the long term health of the battery. Though we have the Lightning set to charge to 90% at home, we will have it go to 100% once per month or so for this reason.

Running to very low SOC: back in the days of NiCad batteries, there was a significance of "battery memory" where if one regularly ran down to say 50%, then after awhile, the battery would run out at that point instead of still having half its capacity remaining. I understand that lithium ion technologies have substantially, if not completely eliminated this effect, but I have a gut feeling that there may be a tiny effect still. I wouldn't recommend on planning to get that low, but occasionally breaking a personal rule like never running it down below 10% (or your personal minimum) shouldn't cause a problem, and may be beneficial.

DC Fast Charging: I've heard some say this causes life-shortening stress on the battery sounding like the way everything that crashes on The Simpsons bursts into flames.

Modern battery technology is designed to take it, but it strikes me that too much could be an issue. By the same token, I suspect it is good for the battery to occasionally get a high power kick in the ass. Use fast charging for road trips and the occasional emergency and do most of your charging on an AC EVSE.

I will note that the high power of DC Fast charging might have more of an effect on your battery's contactors than it's cells. All that power passing through them in the reverse direction. I just had to replace a contactor on one of my FFE battery packs (the FFE has two), and though I don't fast charge very often, and the fastest charge it's ever received was 53 kW, the thought of this on the contactors did cross my mind.

Despite all I've said above, don't forget that your mileage may vary.

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[Adventureboy]

Day to day its 80% in the summer and 90% in the winter. 100% whenever I think i will be putting more miles on that day

Regardless of the safety buffer built into the battery a lower percentage increases pack lifespan. Quick chatgpt answer here for an ER that drives 15k per year.

Charge to 100% daily (≈1.88% annual loss)
• After 10 years: 82.7% remaining → ~17.3% degraded → ~108.4 kWh usable
• After 20 years: 68.4% remaining → ~31.6% degraded → ~89.6 kWh usable

Charge to 90% daily (≈1.63% annual loss)
• After 10 years: 84.8% remaining → ~15.2% degraded → ~111.1 kWh usable
• After 20 years: 72.0% remaining → ~28.0% degraded → ~94.3 kWh usable

Charge to 80% daily (≈1.36% annual loss)
• After 10 years: 87.2% remaining → ~12.8% degraded → ~114.2 kWh usable
• After 20 years: 76.0% remaining → ~24.0% degraded → ~99.6 kWh usable

As with many things ChatGPT, it doesn't tell the whole story. The Depth of Discharge (DOD) is a significant factor in determining the rate of degradation and is perhaps more impactful than the target SOC, given our top-protected packs. Draining your truck to 10% then charging it to 90% weekly, is harder on battery degradation than charging from 75%-90% daily. As the cells charge and discharge, they expand and contract, causing tiny microfractures in the cells that cause degradation. The deeper the discharge, the more microfractures are caused per kWh discharged (it's an exponential scale, not a linear scale). ChatGPT doesn't capture this significant detail in the numbers.

 

[BluesClues]

do some people just not charge everyday? i started just charging weekly to 95% and running it down to 40-60%

 

[fhteagle]

70% summer.
90% winter.

Gets me to at least one (if not two) DCFCs in each direction I'm likely to go in case of an unplanned trip. No, we don't have that many DCFCs per road mile out here...

 

[Adventureboy]

Running to very low SOC: back in the days of NiCad batteries, there was a significance of "battery memory" where if one regularly ran down to say 50%, then after awhile, the battery would run out at that point instead of still having half its capacity remaining. I understand that lithium ion technologies have substantially, if not completely eliminated this effect, but I have a gut feeling that there may be a tiny effect still. I wouldn't recommend on planning to get that low, but occasionally breaking a personal rule like never running it down below 10% (or your personal minimum) shouldn't cause a problem, and may be beneficial.

Memory effect has been eliminated with NMC and LFP technologies. It does more harm than good to drain the batteries really low with the two most common Lithium technologies.

 

[Calvin H-C]

Memory effect has been eliminated with NMC and LFP technologies. It does more harm than good to drain the batteries really low with the two most common Lithium technologies.

I have heard that, but isn't this part of the reason for "0%" on the gauge to really be something like "5%" for the actual battery pack?

I'm just saying that running the battery over the entire range that it's management system is designed for isn't as bad as many seem to think.

 

[Brons2]

If you never charge above 85% you risk masking a module failure. I recommend charging to 100% occasionally for this reason.

I always charge the Lightning and the Mach-E to 100% once a month. I usually try to do it on the 1st of the month. I'm doing it today with my truck as noted earlier in the thread.

 

[chl]

80% works for me

If going on a vacation and it will sit idle, then 40%-50%

I keep the 12V on a trickle charger with an AGM mode when not is use as well to keep it topped off at 100%.

 

[Bigisland Guy]

This topic has been on the forum numerous times. If you care to review your more then welcome to, but I'll go with what our retired battery Guru says and stay the course at 85%.

 

[Adventureboy]

I have heard that, but isn't this part of the reason for "0%" on the gauge to really be something like "5%" for the actual battery pack?

I'm just saying that running the battery over the entire range that it's management system is designed for isn't as bad as many seem to think.

Taking an NMC battery below 20% true SOC starts exponential degradation. Below 10% and the degradation rate ramps up quickly. True, we are protected from the bottom 5% because in some cases, with cell-level discharges down to near 0% , the cells sometimes won't recover. Ford saves us from that (in most cases); however, anything below 15% displayed SOC starts a more aggressive degradation curve per kWh used.

There is little to be afraid of if you take it down to 5% displayed SOC once or twice, but just don't do it on a regular basis. Repeated deep discharges accumulate small amounts of degradation over time and eat away at SOH in little bites at a time. Keeping it above 15% displayed SOC most of the time takes much smaller bites per kWh from the SOH.

 

[Grumpy2]

what our retired battery Guru says

I agree, also remember temperature becomes important to this discussion if the battery becomes really hot. I wonder what he thinks of that EV9 ....

 

[flyin525]

60% Summer
70% Winter

I charge to 100% every 3 months or so for cell balancing if I havent needed 100% for a trip. I keep it plugged in, and try to avoid going below 20% unless absolutely necessary.

This may be a bit overkill but my daily needs dont require a lot of range so it works for me.

 

[Firn]

As with many things ChatGPT, it doesn't tell the whole story. The Depth of Discharge (DOD) is a significant factor in determining the rate of degradation and is perhaps more impactful than the target SOC, given our top-protected packs. Draining your truck to 10% then charging it to 90% weekly, is harder on battery degradation than charging from 75%-90% daily. As the cells charge and discharge, they expand and contract, causing tiny microfractures in the cells that cause degradation. The deeper the discharge, the more microfractures are caused per kWh discharged (it's an exponential scale, not a linear scale). ChatGPT doesn't capture this significant detail in the numbers.

In this case i specifically asked it to consider 15k per year and charged daily.

I didnt put in any of the other factors because they get too varied across users to mean anything. DoD, environmental temp, fast charge frequency, etc all become highly specific

 

[telrod11]

85% Daily, or when I reach 60% or less.

Once a month, 100% whether I need it or not

 

[Adventureboy]

In this case i specifically asked it to consider 15k per year and charged daily.

I didnt put in any of the other factors because they get too varied across users to mean anything. DoD, environmental temp, fast charge frequency, etc all become highly specific

Good reference point. Given Ford's protection approach on the top and bottom, we might yield better results. Time will tell where we land.

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