Another Consideration for Battery Life??

[ranss12]

There have been many comments and predictions about battery life based on ambient temperature (Arizona, Texas, etc), calendar age of battery, charging to 100%/80%, fast charging, depth of discharge, etc, but I don't recall seeing anything that correlates battery life with the average mile/kwh that the driver gets. It seems intuitive that the easier a battery is driven (using the minimum necessary power needed to get up to speed, maintaining a lower average speed, maintaining a steady speed, etc) will reduce the internal battery heating do to internal resistance, but is maintaining a lower battery temperature the only benefit of conservative driving, or are there other effects of conservative driving that will help preserve battery life?

 

[RegGuheert]

Yes, even beyond heating effects, my understanding is that discharging at lower power levels tends to increase the cycle life of a battery.

 

[GregH]

Does anyone know how much of the degradation due to aggressive driving (or charging! DCQC) is due to temperature?

 

[Stanton]

Does anyone know how much of the degradation due to aggressive driving (or charging! DCQC) is due to temperature?

IMHO it's all about the combination of "heat*miles=bars": more of the former means less of the latter to experience a bar loss, but eventually one or the other will get you :evil:

Personally, I avoid DCQC, but I really think ambient heat (climate) is a much bigger detriment to battery life than aggressive charge/discharge.

 

[TickTock]

On a flat road, driving 70mph requires twice as much energy as driving 50mph so is equivalent to driving twice as far as far as the battery is concerned (even worse when you consider the internal heating increase other have mentioned). So yes, how fast you drive will have a big impact on battery life.

 

[DanCar]

The people who first had battery degradation issues were driving at 85 mph. This increases the heat. Driving aggressively will decrease battery life, because it increases number of charge cycles, but the biggest issue with leaf battery has been heat. All the data shows this. Nissan initially said that quick charge would affect battery life, but that hasn't been shown to be an issue compared to heat.

 

[caffeinekid]

You would really have to be pretty heavy on the accelerator to affect it much, ambient temperature notwithstanding. As for miles/kWH, both my wife and I average 4.1 during the 6 month summer that we have here in Houston. One of our Leafs still lost a capacity bar after a year and a half. The other most certainly will since I QC nearly every week day. My anecdotal evidence states that the Leaf is not well suited to ambient temperatures exceeding 85F for most of the year. An ethical manufacturer would not be selling EVs in such regions without a TMS, but that is another glaring elephant-in-the-room discussion going on elsewhere.

 

[GregH]

So if you had two identical batteries and were able to keep them both at constant temperature (say 25C) with an elaborate thermal management system... and you cycled both repeatedly from 80% to 20% and back again a few hundred times... but one was cycled at a 0.5C rate (2 hours) and the other at 0.2C rate (5 hours), which do you think would have more capacity at the end? Same temp, same # of cycles, same (or at least very close) Ah throughput... ? And more importantly.. by how much?

 

[braineo]

The people who first had battery degradation issues were driving at 85 mph. This increases the heat. Driving aggressively will decrease battery life, because it increases number of charge cycles, but the biggest issue with leaf battery has been heat. All the data shows this. Nissan initially said that quick charge would affect battery life, but that hasn't been shown to be an issue compared to heat.

Why would people only drive to 85 mph, 93-94 is much more fun.... :lol:

 

[caffeinekid]

So if you had two identical batteries and were able to keep them both at constant temperature (say 25C) with an elaborate thermal management system... and you cycled both repeatedly from 80% to 20% and back again a few hundred times... but one was cycled at a 0.5C rate (2 hours) and the other at 0.2C rate (5 hours), which do you think would have more capacity at the end? Same temp, same # of cycles, same (or at least very close) Ah throughput... ? And more importantly.. by how much?

Although I am sure there are papers on this, bench tests and probably a relatively simple formula that takes into account the 0.3C rate difference (3 hours) in resting time, I will say that we charge the one that lost the bar exclusively on a 120/20A circuit. The one that has not lost a bar, yet has essentially the same number of miles on it during only a year of ownership AND frequently gets the 480V QC belly rub, has not lost a bar yet.

 

[TickTock]

All of these, although valid, are negligible second-order effects compared to the increase in consumption (charge cycles). Dropping your speed 30% cuts the number of charge cycles in half. So, yes, how fast you drive most definitely impacts battery life.

 

[surfingslovak]

I don't recall seeing anything that correlates battery life with the average mile/kwh that the driver gets.

This has been partially considered in the battery aging model on the wiki. If I recall correctly, Stoaty factored in different number of cycles needed to travel a certain number of miles based on varying average energy economy. What early analysis of field data has shown was a strong correlation between ambient temperature at the place of residence and loss of Gids (60% to 70%). That's why it was discussed so much.

That said, it's clear that there are other factors aside from temperature, but early reports from the field seemed to indicate that 80% vs 100% charging did not matter as much as originally assumed by many, for example. Conversely, the effect of ambient temperature has been seemingly confirmed beyond any doubt. Solar loading seems to be an important contributing factor, as is the average energy economy.

The challenge with the secondary factors is how to properly measure and model those, and verify that this aligns with owner experience in the field.

All of these, although valid, are negligible second-order effects compared to the increase in consumption (charge cycles). Dropping your speed 30% cuts the number of charge cycles in half. So, yes, how fast you drive most definitely impacts battery life.

Indeed. Additionally, the somewhat anecdotal measurements several owners performed seems to support the notion that the pack stays relatively cool during operation, even if the LEAF is driven aggressively.

 

[TimLee]

There was discussion previously, that the LEAF battery may only have 2000 charge / discharge cycles before having 30% capacity loss, although I don't think anyone had good definitive data on this.
The degradation from cycles is going to happen independent of other aging factors such ambient temperature exposure and time from date of manufacture.
So achieving better miles/kWh is going to make the battery get you more miles before needing replacement due to reduced capacity.
TaylorSFGuy lost his first capacity bar a little under 80,000 miles in the ideal ambient Pacific Northwest, doing high miles per year, which reduced time from manufacture capacity impacts.
I don't know his miles / kWh, but if he was at 4 miles /kWh, that is around 900 cycles.
Bit unclear exactly what the capacity loss is for one bar, but something in the 15% to 20% range.
So his experience on capacity loss does seem to fit fairly well with the 2000 charge / discharge before having 30% capacity loss that was mentioned previously.

 

[GregH]

Indeed. Additionally, the somewhat anecdotal measurements several owners performed seems to support the notion that the pack stays relatively cool during operation, even if the LEAF is driven aggressively.

From my experience if the ambient air is cool relative to the pack, then yes driving seems to "air cool" the pack enough to compensate for moderate heating due to discharge (ie driving in the 3.5-4.0 mi/kWh range). Of course how hard you drive it and how much cooler the air is all plays a part.
Charging will always generate a lot of heat.. Even 3.3kW charging.
When parking I've learned to pay more attention to where the shade WAS rather than where it IS. The cabin can get pretty toasty without heating the battery but if you park on some warm pavement that all gets absorbed. I used to try to move my car when the morning shade left it exposed to the sun.. now I'm less reactive (I don't mind letting it sit in the sun for an hour or two) because the pavement underneath is still cool, the pack barely warms at all even though the cabin is baking.

 

[GetOffYourGas]

Indeed. Additionally, the somewhat anecdotal measurements several owners performed seems to support the notion that the pack stays relatively cool during operation, even if the LEAF is driven aggressively.

I recently purchased an OBDII reader, and have been monitoring the battery temperature (among other things). Last weekend, when I left the house the battery was about 75F. Ambient temperature was at 91F. I had been parked in the cool garage overnight, and it wasn't nearly as hot the day before. The surprising thing was that after driving for about half an hour, at about 4.5 m/kWh, the battery temperature was at 78F. In other words, it had risen very little despite a somewhat significant temperature delta from ambient as well as being actively used. After driving, I topped off the battery (last stop before a 90 mile leg). After charging from ~80% to full, the battery was at 79F. The ambient temperature was still over 90F. This suggests to me that 1) modest driving causes very little heating, 2) the pack is fairly well insulated from ambient air and 3) even 3.3kW charging adds very little heat.

Again, this is a single data point, so take it for what it's worth. I was just pleasantly surprised at how well insulated the battery truly is.

 

[DaveinOlyWA]

All of these, although valid, are negligible second-order effects compared to the increase in consumption (charge cycles). Dropping your speed 30% cuts the number of charge cycles in half. So, yes, how fast you drive most definitely impacts battery life.

this is the only post in this thread that makes sense. if you charge to 80% daily and drive 60 mph verses 70 mph, you will go X further driving 60 mph before losing first bar than if you drove 70 mph.

I noticed that few who reported a bar missing said how fast they drove. As time goes by, I am driving slower partly due to loss of range but mostly because I dont want to stop to charge and there is 5-10 days a month where I can drive 55-58 mph and make it home verses driving 60-62 mph and having to stop for a 10 minute boost. I'd much rather drive the 55

 

[TomT]

How do we know this?

The people who first had battery degradation issues were driving at 85 mph.

 

[TomT]

The pack has a lot of thermal mass and changes temperature slowly...

The surprising thing was that after driving for about half an hour, at about 4.5 m/kWh, the battery temperature was at 78F. In other words, it had risen very little despite a somewhat significant temperature delta from ambient as well as being actively used.

 

[johnqh]

You would really have to be pretty heavy on the accelerator to affect it much, ambient temperature notwithstanding. As for miles/kWH, both my wife and I average 4.1 during the 6 month summer that we have here in Houston. One of our Leafs still lost a capacity bar after a year and a half. The other most certainly will since I QC nearly every week day. My anecdotal evidence states that the Leaf is not well suited to ambient temperatures exceeding 85F for most of the year. An ethical manufacturer would not be selling EVs in such regions without a TMS, but that is another glaring elephant-in-the-room discussion going on elsewhere.

I don't think TMS would make any difference as your battery will still sitting at 85F during the day when parked.

 

[dgpcolorado]

From my experience if the ambient air is cool relative to the pack, then yes driving seems to "air cool" the pack enough to compensate for moderate heating due to discharge (ie driving in the 3.5-4.0 mi/kWh range). Of course how hard you drive it and how much cooler the air is all plays a part.
Charging will always generate a lot of heat.. Even 3.3kW charging...

I've seen this, even had the temperature go down during generally downhill runs at cool ambient temperatures (>10ºF below battery temp). However, I have to deal with steep hills and the temp does rise with the high discharge rates required, typically 20kW or more at 25 to 35 mph. Going up moderate grades at 60 mph is a sure way to raise the battery temperature IME. I think the fact that I have to use high discharge rates every time I leave home might be a factor in my battery degradation in what is otherwise a mild climate for a LEAF. I think that abasile has seen this also.