Best practices to preserve battery life??

[paw160]

I think if I were going to leave the vehicle for an extended period of time, I would actually disconnect the main and 12V batteries. This minimizes parasitic loads draining the batteries while in storage.

It's ok to let the battery get cold, but you should warm it up and then charge it before the first use.

 

[EVfuture]

Thanks for the posts. The car's in my garage and somewhat protected from the lowest temperatures, but I think I'll leave it plugged in on the 110v based on your advice and what the manual says. EVA, I will try leaving the car as you suggested to see the effect on the 12v battery. I will also check into having the recall/update done asap.

 

[michael]

I apologize for making what is in effect a double post since I made very similar comments in a thread about why I think Ford needs to provide a means to provide a maximum charge level, but it pertains here as well so I will do so anyway.

By way of background, I have a three year 58000 mile lease, my daily commute is 40 miles to work, and between 40 and 60 on the way home, depending on stops I need to make. I charge up at work and at home.

I have read numerous papers from the Department of Defense, National Renewable Energy Laboratory, JPL and others. I work at a company that uses lithium batteries extensively, and I've talked to the engineers who use them. I have concluded that for maximum long term battery health

1. Keep the batteries cool ( everybody knows this, no surprise to anyone)

2. Keep them at a low state of charge as long as practical. In other words, charge them up so they will be ready to go just before you need them, rather than immediately upon returning from a trip

3. Charge them only to the level that allows you to complete your trip and arrive at a charging station with a reasonable ( maybe 20-30%) state of charge. Try to keep centered around half charge.

4. The effects of temperature extremes are most harmful at high levels of charge

5. The fact that Ford limits what we call 100% charge to something less than actual full charge definitely helps, but every EV manufacturer does this to some extent. For best battery longevity, lower is better. The army found that running batteries between 50 and 0 % provided better life not only than between 100 and 50, but also better than between 75 and 25. I was surprised to see this.

6. We all know that running a lithium battery flat kills it, but this seems to have created the idea that running them low is unhealthy. The research refutes this.

7. A lot of people will agree that the car shouldn't be stored for long periods with the battery fully charged, but feel that keeping it charged overnight is fine. This doesn't make sense to me...hours are cumulative. Degradation is a chemical reaction. 7 hours a day for 24 days is no different than 7 days of 24 hours. They are both 168 hours of degradation. The takeaway is that just-in-time charging is better for the battery than end-of-day charging.

I know the first point is fairly well accepted, but I expect disagreement from some on the other points. So I offer them for consideration by those who, like myself, need to keep their batteries as healthy as possible.

Based on my usage, I use the value charging feature to start charging at 5 every morning. I reprogram value charging to stop when the charge reaches 80-85%. At the office I use a 3 kW portable charger so it takes most of the day to get back to 80-85%. In this way my charge generally ranges between 80-85 on the high side and 20-35 on the low side. I think this is the best I can do.

 

[davideos]

This sounds reasonable, thanks for the information. I see that with some thoughtful maintenance the battery life could be extended, but can we quantify it in any way? If a battery were kept at full charge for 1 hour, what is the percentage of degredation? If we knew that, we could compute the cost of keeping a batter charged. This becomes important for 2 reasons I can think of:
1) If I charge just before I go to work, the cost of that charge is 50% more costly than charging between 12a and 6a. Over time, would this practice cost me more in the long run vs purchasing a new battery X months sooner?
2) Convenience of keeping a battery charged. Sometimes my battery usage is predictable; however, sometimes, it has paid off keeping the battery charged for unexpected trips. The alternative is to take the ICE car which costs much more money to operate...or charge the car at peak rates which is more than 2x the super-off-peak rate. The value of this would be a little bit harder to compute as it is a less predictable occurance.

Anyway, is there any data showing the amount of degredation when the battery is 100% charged (which for the FFE is more like 90%) vs a 50% state of charge?

 

[paw160]

I would strongly caution against the temptation to never fully charge the battery. Lithium ion batteries are made of a large collection of small battery cells. Each of these cells gain and discharge electricity differently. This is due to small chemical variances among cells. As a result cells can get out of balance. This critical cell balance is restored during the charging process by the battery management system. In addition, balancing only happens effectively near the end of charge.

Most lithium ion battery distributors will recommend periodically discharging to <20% and then fully charging to 100%.

This has an additional benefit in that it is easier to do coulomb counting during charging rather than discharging. Most battery systems that I've worked with need this full cycle to accurately monitor capacity.

 

[hcsharp]

...
1. Keep the batteries cool ( everybody knows this, no surprise to anyone)
...
3. Charge them only to the level that allows you to complete your trip and arrive at a charging station with a reasonable ( maybe 20-30%) state of charge. Try to keep centered around half charge.

Thanks for your recommendations. How do you reconcile the fact that 1 and 3 work against each other? It becomes a matter of priorities as to which is worse - heat or state of charge (SOC). Based on everything we've both read, heat is worse, especially if you never charge above 90% SOC to begin with (like the FFE). I've read a lot of well funded studies and virtually all of them simulate conditions that are different than we have in a Li-ion powered automobile. There are 2 primary differences in how we use batteries.

While it's true that storing a Li-ion cell at a lower SOC is better for it, the effect is minimal below 85 to 90% SOC, depending on chemistry and other variables. Since the FFE (and virtually all EVs) only charge up to about 90% to begin with, this problem is almost eliminated. This is especially true, as you mentioned, if the battery is kept cool.

The other major difference between most of the studies and an EV application is how energy is drawn from the cells. In your commute to work you will use the same amount of energy regardless of whether you start at a high SOC or a medium SOC. Drawing the same amount of power from a battery at a lower SOC requires, by definition, more amps. More amps equals more heat. But most lab and field studies looking at SOC vs longevity didn't consume power in the same fashion. Instead, many of them tried to keep temperatures the same to be more scientific and eliminate heat as a factor that might influence results. The difference can be dramatic. Driving the same speed at 3v/cell requires 30% more current than driving at 4v/cell. In my other EV, 2 clicks on a touch screen will display battery temp, motor temp, and inverter temp (another feature Ford should have). It's easy to observe the motor and battery temps climbing much faster at lower SOC.

Some people have made a good argument that Ford's thermal management is good enough that it prevents any heating effect at lower SOC. Unfortunately it's not completely true. It takes time to conduct heat out of the large prismatic cells that Ford is using. Your coolant temps rise while you are driving and the cells are always warmer. Worse, when you arrive home your cells are usually at their warmest. If you don't plug in immediately, you end up soaking your cells hot for many hours until you charge.

[edit: just noticed paw160 already addressed content of this paragraph.] There's another potential problem with your practices that you are ignoring and is not generally addressed in any of the studies. That is the subject of balancing cell voltage. I think the motor operates on about 375 volts? A lot of cells are stacked in series and the curtain gets closed when the weakest group of cells in series reaches the lowest allowable voltage. Most EVs balance their cells when they are resting near their highest SOC because it's difficult to do it effectively while you're charging, driving, or at a low SOC. Driving without well-balanced cells reduces longevity because the weakest cells are taxed the hardest, ultimately shortening their life faster. I called this a "potential" problem because we don't know much about Ford's electronics to know when and how they balance but it's likely that your cells are less balanced than somebody who charges full every day.

I've been advocating the best practice for longevity (not necessarily practical) would be to cool your battery as soon as you stop driving by starting a slow charge (say 12-14A 240v). Slow enough not to heat the pack or raise it to a high SOC, but enough so it activates the A/C cooling system until the pack is cool. Then sit at a still low SOC, then do a Value Charge so it's full about 15 min before you leave. That allows a little time to balance, and minimizes the time at the FFE's highest SOC while also minimizing the heat generated while driving.

7. ...The takeaway is that just-in-time charging is better for the battery than end-of-day charging.

What if your car ends up sitting hot for several hours as a result? Do you think your advice is only good as long as you plug-in to cool it off before it sits until just-in-time starts?

 

[hcsharp]

This sounds reasonable, thanks for the information. I see that with some thoughtful maintenance the battery life could be extended, but can we quantify it in any way? If a battery were kept at full charge for 1 hour, what is the percentage of degredation? ...

Probably nothing. An interesting read is the study that Plug In America did on the Tesla Roadster.
http://www.pluginamerica.org/surveys/batteries/tesla-roadster/PIA-Roadster-Battery-Study.pdf
There were many owners who went to great lengths to prolong battery life, but ended up in the middle of the spectrum along with those who charged full at 70A every day as soon as they got home. The sample size was small for those who tried to prolong life so it's hard to draw conclusions, but mileage was the overriding factor in degradation. Some of us try to prolong battery life anyway because we just can't help it.

 

[davideos]

This sounds reasonable, thanks for the information. I see that with some thoughtful maintenance the battery life could be extended, but can we quantify it in any way? If a battery were kept at full charge for 1 hour, what is the percentage of degredation? ...

Probably nothing. An interesting read is the study that Plug In America did on the Tesla Roadster.
http://www.pluginamerica.org/surveys/batteries/tesla-roadster/PIA-Roadster-Battery-Study.pdf
There were many owners who went to great lengths to prolong battery life, but ended up in the middle of the spectrum along with those who charged full at 70A every day as soon as they got home. The sample size was small for those who tried to prolong life so it's hard to draw conclusions, but mileage was the overriding factor in degradation. Some of us try to prolong battery life anyway because we just can't help it.

I think that's where I sit; just value charge and keep it plugged in. When I get home after driving on a hot day and I plug it in, the fan in the motor compartment turns on...I assume, cooling the batteries. It then charges later at midnight. Also, if I get down low, like the other day (9 miles remining), and I plug in, the car will charge regardless of the value charge setting. I think it brings it up to 15%.

 

[michael]

I'm glad my comments stimulated this discussion.

At first I too was concerned that balancing might require a full charge, but then I realized that even with so-called 100% charging, the battery isn't fully charged in the normal sense. And no EV battery is. This is even more true with Ford's hybrids. So for one reason or another, it would seem that whatever cell balancing might be needed, having a full charge is not a requirement .

The concerns about lack of thermal control while stopped but not charging are not really justified. I keep the car plugged in and use the value charging capability to delay charging til I want it to stop. The TMS is operating.

The concerns about increased heating at lower voltage are justified, but the can be resolved by slowing just a very little bit. Slowing from, for example, 70 to 65 reduces the power requirement to 80% (cube of the speed). If we model the battery as a variable (based on SOC) voltage source with a constant internal resistance, the heat generated in the battery would reduce by the square of the power reduction...to 64% of the 70 mph value.

To the question about how much capacity would be lost in an hour at full charge.I can't say, but less than if held at full charge for 8 hours. And more than if at a lower SOC.

As I stated, I expect disagreement on many of these issues but based on my reading I think this is the way to go if extended battery life is important to one.

 

[oilman]

This is all great discussion, but I leased the Focus so I don't have to worry about eeking out every last bit of battery life. In fact, I tell people that I preferred the Focus over the Leaf because of the active battery temperature management. When I was lurking on the Leaf forums it seemed that well over half of the discussion was about battery temperature or capacity degradation. I want to be able to drive the car as required at any time without worrying about the range I have left. That means I usually plug in when I get home after my 20 mile commute (although I often use the value charge) so I am topped off for the next day. EVs will not become mainstream if we have to worry about fiddly batteries, so I have to rely on the engineers to minimize the impact as much as they can. This all comes down to how much capacity is lost or maintained even with perfect habits. In the end, if the difference is 5% or so, it won’t really be worth it in the end. Just my opinion.

Oilman

 

[jeffand]

The Focus battery pack is 325 volts.
The battery pack doesn't like heat over 90 degrees. Since the car can use the air conditioner to cool the battery pack does give it an advantage over the Leaf.

 

[WattsUp]

the car can use the air conditioner to cool the battery pack does give it an advantage over the Leaf.

...as well as heat the battery pack when its cold for same.

 

[hcsharp]

At first I too was concerned that balancing might require a full charge, but then I realized that even with so-called 100% charging, the battery isn't fully charged in the normal sense. And no EV battery is. This is even more true with Ford's hybrids. So for one reason or another, it would seem that whatever cell balancing might be needed, having a full charge is not a requirement .

LOL I don' think you can draw that conclusion based on the hybrids. The parallel hybrids are designed to use the middle 20% of the battery so obviously they're not the same. The serial hybrids have smaller batteries and are designed for quick charge/discharge cycles repeatedly when the engine is on. And also must have a provision for the cases where it's never plugged in at all, unlike a pure BEV. The key word is effectiveness. The higher your SOC, the more effective the balancing is. It can't balance at all while driving. It's extremely difficult while charging. It's most effective when performed right after a full charge which is why BEVs commonly do it then. If you unplug while it's still charging and drive right away it's virtually impossible for it to ever balance at all, which ultimately is bad for longevity.

The concerns about lack of thermal control while stopped but not charging are not really justified. I keep the car plugged in and use the value charging capability to delay charging til I want it to stop. The TMS is operating.

I agree that's a good practice (except stopping the charge before it's done). I think the discussion had more to do with using different methods of managing time-of-use charging that didn't necessarily involve plugging in right away when you get home, or plugging in without enough power to let the TMS run. Some of us can't use Value Charging or Go Times right now because Ford broke it and waiting for them to fix it.

The concerns about increased heating at lower voltage are justified, but the can be resolved by slowing just a very little bit. Slowing from, for example, 70 to 65 reduces the power requirement to 80% (cube of the speed). If we model the battery as a variable (based on SOC) voltage source with a constant internal resistance, the heat generated in the battery would reduce by the square of the power reduction...to 64% of the 70 mph value.

LOL that doesn't give any advantage to driving at a lower SOC! I can do the same thing after charging full. If we're both driving the same speed, your car will heat the battery more than one at a higher SOC. And I think we both agree heat is a far bigger factor in battery degradation than SOC, especially if the system never charges to theoretical 100% in the first place.

I agree it's good to have these discussions. Part of the fun of being early adopters. Keep in mind most of the studies you read are not very applicable to EVs that don't ever charge full, have different thermal issues, and need to balance after they finish charging. If you read the Tesla Roadster study you might get a different perspective.

 

[hcsharp]

the car can use the air conditioner to cool the battery pack does give it an advantage over the Leaf.

...as well as heat the battery pack when its cold for same.

Since Nissan came out with their "winter package" for the Leaf, it can heat the pack. The problem is heating with air/convection is far less efficient than with liquid, even if you don't use a heat pump. Another reason the FFE get's better range in very cold conditions.

 

[Arthur]

The Focus battery pack is 325 volts.
The battery pack doesn't like heat over 90 degrees. Since the car can use the air conditioner to cool the battery pack does give it an advantage over the Leaf.

Some people say that the FFE battery consists of 98 LG Chem lithium-polymer pouch-type cells, that are 60Ah each and that are connected in a single series circuit. The nominal voltage of each cell is 3.7V and the voltage of a fully-charged cell is 3.9V. Therefore, 98 cells X 3.9V/cell X 60Ah = 23kWh (theoretical total battery capacity, if the software allowed the cells to charge fully).

Some of the characteristics and manufacturing processes for these cells can be seen in the three promotional videos, on thy Automotive Battery section of the LG Chem website: http://www.lgchem.com/global/vehicle-battery/car-batteries