Which is worse for the battery? 3 charging scenarios

Which is worst for battery health? I hear things like do not charge to 100%, do not deplete the battery constantly, do not do this and that. Ok, so I will start with 3 common charging scenarios that is usable:

The variables in play are: num of days of charging, 80% vs 100%, usage pattern and opportunistic charging.

1) 7 days per week, charging to 80%, usage of battery never goes below 5 bars, always charging opportunistically. This means, there is at least a minimum of 2 times per day the car is plugged in.

2) Alternating 3 days per week: charging to 100%, usage of battery always goes down to 3 bars, the car may only get plugged in 3-4 days per week and opportunity charging is limited to emergencies only.

3) Alternating 4 days per week: charging to 80%, usage of battery always goes down to red-basically 1 or 2 bars constantly, the car may only get plugged in 3-4 days per week and opportunity charging is limited to emergencies only.

Let's see what others think which scenario in an order, is worst for the Leaf's long term battery longevity.

From what I know, I think 1 is clearly better than 2 or 3.
Not sure which of 2 vs 3 is better though.

I think it may depend on how long you leave the vehicle at 100% before driving in scenario 2.
Also, how hot it is.

1 is certainly worst. I don't think it makes a lot of difference between number 2 and 3, however... I charge to 80 percent except for those occasions when I'll need more range, and I plug in at home whenever I am there, so I charge to 80 percent at least daily unless I have not used the car in the proceeding day for some reason.

I would want to cycle the battery between 2 and 10 bars, and I think #3 is closest to that protocol. Keeping the battery around the middle is desirable, but #1 could translate to a higher average pack voltage over its lifetime. I would not use #2 and only charge to full when needed, make sure that the charge completes right before my trip and the Leaf does not sit full for very long.

From what I understand, the battery wants to sit in the middle of the range most of the time.

I see nothing wrong with number one. As long as you're staying at/under 80% I don't believe that trying to cycle the charge lower by skipping charging opportunities will have any significant impact. Skipping charges certainly WILL result in missed driving opportunities, IMHO.

mxp - let's separate the guesses and fear from facts. It won't get us all the way to the goal but will get us very close.

There is no such thing as a single 'lithium' battery. Folks try to lump anything with lithium into one group and manage them the same way - and that's a recipe for disaster. The good news is that we do not have to worry about managing the battery because Nissan engineers have done the work and designed a 'Joe Public-proof' computer system.

The things that shorten battery life have already been taken care of - we cannot overcharge, we cannot over-discharge, we cannot charge too quickly or use energy too quickly, and we cannot overheat the battery. These are the biggies. Everything else we can consider is in the small area of diminishing returns.

Considering your list of three options - if three cars are treated to one each of the options, I don't expect there to be a significant difference in cycle life or capacity at the end of the test.

If one absolutely feels that they cannot allow the system to work as designed - if they really need the entertainment or hobby of 'managing' their battery, then don't use the top or bottom bar on the car's 'fuel gauge.' It probably won't do much for the battery, but it'll make the owner feel like they're doing something.

Doesn't seem like we have a strong consensus. The "rules" for best battery health don't seem to be well understood by all.

AndyH said:

The things that shorten battery life have already been taken care of - we cannot overcharge, we cannot over-discharge, we cannot charge too quickly or use energy too quickly, and we cannot overheat the battery. These are the biggies. Everything else we can consider is in the small area of diminishing returns.

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You've said this before, yet Nissan gave us a bunch of suggestions in the owner's manual, plus "long life mode" (AKA 80% charging). Why would they do that if none of it matters?

AndyH said:

Considering your list of three options - if three cars are treated to one each of the options, I don't expect there to be a significant difference in cycle life or capacity at the end of the test.

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Andy, nice write-up! I'm not sure if I agree with this statement however.

Charging to full all the time and depleting the pack all the way to turtle will negatively impact battery life. Yes, Nissan, in its infinite wisdom, has taken care of the extremes, but shallow cycling your battery will significantly limit capacity fade. I believe that a 50% depth of discharge cycle is often mentioned as desirable and it looks like both the Volt and the plugin Prius are using something close to that protocol as well. Based on what we have all gathered on this forum, a 50% DoD cycle most likely corresponds to something between 2 and 10 bars.

Obviously, there is still the issue of calender life, but that's a separate topic.

surfingslovak said:

Based on what we have all gathered on this forum, a 50% DoD cycle most likely corresponds to something between 2 and 10 bars.

Obviously, there is still the issue of calender life, but that's a separate topic.

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...and your choice is (1, 2, or 3)? I'm amazed how much disparity there is in these answers. If I had to choose, I'd go for #1 (although I won't do much "opportunity charging"). Remember, a half-cycle charge plus a half-cycle charge is the same as one FULL cycle charge from the battery pack's perspective, so this scenario doesn't count against "total cycles" as much as it appears.

My personal rule of thumb: Always try to save the top two and bottom two (red) bars for emergencies, or rare longer distance trips.
Also, I set timers to get to 80% just before I need to leave in the morning, so it stays closer to 50% most of the time. When I get to work, it is down to around 50% SOC and stays that way all day. When I start heading home, it runs down near the bottom bars but it doesn't stay there too long as it starts the nightly recharge soon afterwords.
If I ever take any side trips at lunch, or on the way home, I seek opportunistic charging to avoid dipping into the bottom two bars.

So basically:
Trying to leave the car near 50% SOC when parked as much as possible.
Trying to charge up to only 80% just before I need to start driving.
Getting back on charge as soon as possible if I get down near 2 bars left.
Use opportunistic charging when taking side trips that threaten to upset the above routine.

Regarding cycle life - I don't think of partial / opportunistic charging as burning a "cycle".
If I have a chance to go from 40% SOC to 60% SOC opportunistically, I would gladly take it instead of running down to 20% SOC before going on a nightly charge cycle.

By the way, the whole charge routine philosophy I had adopted was very different when I was driving the NiMH Ford Ranger before. In that case there was some minor "memory effect" with the cells that warranted some deeper discharge behavior on purpose.

I place my confidence in a mix of all three. Charge mostly to 80% daily. But periodically go to 100%. And don't worry about getting into the last two bars every now and then. Based on nothing just my WAG. Moderation and diversification is my policy.

Stanton said:

...and your choice is (1, 2, or 3)?

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I posted my answer earlier in the thread, I'm sorry if that wasn't obvious. I believe that #3 resembles a 50% DoD cycle, and that's what I would vote for. There is nothing wrong with #1 per se, but only if the battery spends more time at six bars than at 10 bars.

TEG said:

My personal rule of thumb: Always try to save the top two and bottom two (red) bars for emergencies, or rare longer distance trips.

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+1 Great write-up!

surfingslovak said:

AndyH said:

Considering your list of three options - if three cars are treated to one each of the options, I don't expect there to be a significant difference in cycle life or capacity at the end of the test.

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Andy, nice write-up! I'm not sure if I agree with this statement however.

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No worries!

surfingslovak said:

Charging to full all the time and depleting the pack all the way to turtle will negatively impact battery life.

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How do we know? How will it negatively impact life?

surfingslovak said:

Yes, Nissan, in its infinite wisdom, has taken care of the extremes, but shallow cycling your battery will significantly limit capacity fade. I believe that a 50% depth of discharge cycle is often mentioned as desirable and it looks like both the Volt and the plugin Prius are using something close to that protocol as well. Based on what we have all gathered on this forum, a 50% DoD cycle most likely corresponds to something between 2 and 10 bars.

Obviously, there is still the issue of calender life, but that's a separate topic.

Click to expand...

Please completely disregard hybrid batteries and their ~50% depth of discharge. A cell tailored to hybrid use has a shorter cycle life and can handle significantly higher rates of charge/discharge - hybrid power pulses. An EV cell is tailored to lower charge/discharge rates and longer cycle life.

For one of many comparisons, contrast the specs from AESC:
Hybrid: http://www.eco-aesc-lb.com/en/products/Products-e.files/Specifications-e.htm#cell_performance_HEV
EV: http://www.eco-aesc-lb.com/en/products/Products-e.files/Specifications-e.htm#cell_performance_BEV
They have different capacities, different nominal C rates (.3 VS 1), different voltages, different charge/discharge curves... They are different cells.

For cycle life and calendar life, if driver one charges to 100% and drives to work and returns home, and if driver two charges to 80%, drives to work, recharges to 80%, and drives home, they've both used the same fraction of the cycle life and will have the same calendar life.

Sure - if only drives 10 miles per day, charge to 80% and only recharge once a week. It might do something for battery life - time will tell.

Yes - if we charge to 100%, keep the car parked in a hot garage, and only use the car on weekends, we may have a shorter battery life. But that's more about storage than charging to 100%. (And we cannot charge to 100% or discharge to 0% anyway - we're very likely running between 15% and 95% - and this is exactly the ~80% we should use for this type of cell. This type of cell doesn't carry most of its energy in the middle - it carries it nearer to 'the top.')

I certainly don't claim to know everything about lithium, and still haven't tested one of Nissan's cells on the bench. But I do have about five years of experience testing/evaluating various lithium cells on the bench and on the road , and my daily driver is a LiFePO4 powered motorcycle.

davewill said:

AndyH said:

The things that shorten battery life have already been taken care of - we cannot overcharge, we cannot over-discharge, we cannot charge too quickly or use energy too quickly, and we cannot overheat the battery. These are the biggies. Everything else we can consider is in the small area of diminishing returns.

Click to expand...

You've said this before, yet Nissan gave us a bunch of suggestions in the owner's manual, plus "long life mode" (AKA 80% charging). Why would they do that if none of it matters?

Click to expand...

From my cell-level and battery-pack level view, I think it's more about the corporate attorneys than battery limitations.

As soon as they say "charging to 100% is fine for normal use" someone will charge to 100% and leave the car parked in their garage in S Texas every year for six months then complain because of reduced capacity in 6 years rather than 10.

In the end, we have to standardize on a definition of 'cycle' and decide what we really want - miles or time. If we consider (as cell manufacturers generally do) that one cycle is the approximately 80% of ultimate capacity allocated to the consumer, then we may get, for example, 2000 cycles charging to 'consumer 100%' and discharging until we stop on the side of the road. If we ignore capacity loss for a minute, that 2000 cycles at 90 miles per day might be 180,000 miles of service. If we elect to only use 50% charge at any one time for about 45 miles per 'new cycle', we may get 3000 'new cycles' - for about 135,000 miles of service. (I don't know how cycle VS. discharge corresponds for the AESC cell, but the 2000/3000 number is accurate for a decent quality LiFePO4 cell, so I didn't completely pull the numbers out of my nether region. )

Thanks to ALL who initially responded... including Andy's thought provoking views!
Please continue to add in your comments.

I am intrigued by all the data points presented so far, and I hope others will chime in their perspectives.

I am aware that there isn't going to be one correct answer, but the intent of the questions was to encourage people to state their view and the rationales behind those answers based on how they feel of the Leaf's capabilities in all your own personal driving/charging experiences.

I do wish to make a point that the Leaf manual did have about the 80% charge option for battery longevity and that should be a major consideration. I mean, if it wasn't meant to be a consideration, why would they say it in the manual right?

In my personal view, I felt that since the 80% charge is should not be ignored (since Nissan says so... ;-)) but in my case, I am forced to drive it down to red bars every time I charge it up to 80% (commute is 60 miles roundtrip). So, the common knowledge aka: "... never run lithium batteries to low..." scares me even though I am keeping the 1st rule which is to charge to 80%.

Now, if I break the 1st rule of 80% charge, then I get to keep the lithium batt from being discharged to a low point.

It definitely confusing for me at this point.

PS: Do keep up the discussion and views coming in!

TEG said:

My personal rule of thumb: Always try to save the top two and bottom two (red) bars for emergencies, or rare longer distance trips.

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But surely everyone agrees that with the "new bars" there are one or more invisible bars at the bottom. It seems to me that we are converging on 1.5 invisible bars. If the (probably slight) negative effects are the same on both end, that suggests you should save the top two bars and half of the very bottom visible bar for special occasions.

Based on that, my rule is to charge to 80% unless I need more, and avoid getting the Low Battery Warning, unless I need to squeeze a little extra out of the battery. Dropping to one bar doesn't bother me a bit.

Ray

mxp said:

In my personal view, I felt that since the 80% charge is should not be ignored (since Nissan says so... ;-)) but in my case, I am forced to drive it down to red bars every time I charge it up to 80% (commute is 60 miles roundtrip). So, the common knowledge aka: "... never run lithium batteries to low..." scares me even though I am keeping the 1st rule which is to charge to 80%.

Now, if I break the 1st rule of 80% charge, then I get to keep the lithium batt from being discharged to a low point.

It definitely confusing for me at this point.

PS: Do keep up the discussion and views coming in!

Click to expand...

It's correct that over discharging (or reversing) a cell can kill it or at least give it plenty of gray hair and age spots. And it's correct that most types of lithium cells will give up some cycle life if over charged. But - (here's the important part!) - the only way a Leaf cell can be discharged close to zero or taken close to over charge is if the management system dies. This car is not a laptop. It's not a LiPo pack in a radio controlled airplane (no BMS!). It's not a LiFePO4 pack in a Chinese scooter.

I'd charge to 100% before my 60 mile drive - especially if there was a chance of a side trip for milk and eggs on the way home.

This is how I operate my lithium-powered motorcycle - and it took me a few years of bench testing with calibrated equipment to build up to this comfort level, so I can absolutely understand the fear of the unknown! I've been taking some classes at the local university the past few months. I use just under 50% of battery capacity for one round trip. While I could squeeze two trips into one charge, I ride one round trip and plug it in. If I come home for lunch between classes, I plug it in for the second trip. I'm more comfortable keeping some extra 'fuel' in the tank as it gives me some flexibility later in the day when my brain is full. I know that my 100% charge is really only 80% - and that's the sweet spot for a long battery life with a LiFePO4 battery. I know that my management system will not allow me to over charge or over discharge the battery - I don't have to think about it day to day because I thought about when I wired the management system. Now instead of watching the gauges, I can think about the brunette in the red Benz...I mean I can focus on riding and keeping proper distances. :lol:

mxp said:

In my personal view, I felt that since the 80% charge is should not be ignored (since Nissan says so... ;-)) but in my case, I am forced to drive it down to red bars every time I charge it up to 80% (commute is 60 miles roundtrip). So, the common knowledge aka: "... never run lithium batteries to low..." scares me even though I am keeping the 1st rule which is to charge to 80%.

Click to expand...

I think you are fine, driving it down to the red bars is also fine.

If you need it then charge to 100%, but do it just before you use the car so the battery does not stay at that level for long. Program the car to stop charging at 80%, when you get up in the morning restart the charge to 100% and eat breakfast.. it should be at 100% by the time you are ready.

It is my belief that Nissan leaves about 11% capacity hidden below the turtle shutdown, it never lets you get below turtle shutdown.. that in combination with an 80% charge is a very conservative 70% DOD cycle, very good for prolonging battery life. So the best advice is to just follow the manual, and also move out of Phoenix