Does Running Battery Very Low Affect Capacity Over Time?

[Stoaty]

Reading through abasile' post it occurred to me that he could put his Leaf into neutral on a descent if he wanted to avoid hitting the battery. I've noticed that there was no regen when breaking in neutral. I'm sure that it's counterproductive on some level, but it would help alleviate battery concerns if that was the primary goal.

Yes, but he would either burn out his brakes or hit 100 MPH on steep, curving mountain roads. Not a good choice in my opinion.

[abasile]

Reading through abasile' post it occurred to me that he could put his Leaf into neutral on a descent if he wanted to avoid hitting the battery. I've noticed that there was no regen when breaking in neutral.

That is true, but for safety reasons since friction brakes heat up, you don't want to rely exclusively on fiction braking for long mountain descents. An alternate approach, which I sometimes employ, is to drive fast (55 mph) on the descent. That way there's more wind drag and less regen. Plus it's fun.

I should also say that I'm not *that* concerned about battery degradation due to regen. One of our big mountain descents is still significantly less stressful than a Quick Charge session, since the regen is not continuously maxed out, is spread over a longer period of time, and involves less total energy into the pack. And we only do it once or twice per week. It's just something to be aware of if you are an EV geek...

Also, sorry to have strayed from the topic. The big point is, if you really want to maximize battery longevity, we believe it's best to try to stay in the center, or somewhat below the center, of the SOC range as much as possible. But more importantly, use the car. If using the car requires charging to 100% or draining to almost empty, then do it.

[surfingslovak]

I should also say that I'm not *that* concerned about battery degradation due to regen... It's just something to be aware of if you are an EV geek...

Yes, thank you for clarifying that. I haven't done any mountain driving and I'm looking to put some of the things I have learned here into practice on my next trip to Santa Cruz.

My commute is very short, only about 7 miles one way, and I found myself keeping the battery at a relatively low state of charge on weekdays. Much like yourself, I'm aware that on a day-to-day basis it won't make any difference, but the engineer in me likes to optimize the protocol. Unfortunately, there are numerous factors playing into this and without a proper model or some lab testing, it's tough to identify best practices and quantify any long-term benefit.

Based on what I have seen so far, I would not worry about running the battery down to the low battery warning, and even a bit beyond that. That being said, I would try to keep it above two bars if I can, but if I needed the extra range, I'm confident that no disproportional harm will be done to the battery. I agree that internal resistance will be higher and more heat will be generated, but it should all be relatively immaterial. There is some indication that it might be a good idea to avoid hitting turtle on a regular basis, but I doubt that anyone would want to do that anyway. Unfortunately, I have no data to quantify the effect this would have on the battery.

[TomT]

Actually, that is one of the reasons why the Leaf has such massive brakes for its size, performance and weight; to handle such situations of no regen on long, steep downhills. The brakes are more than up to it.

Yes, but he would either burn out his brakes or hit 100 MPH on steep, curving mountain roads. Not a good choice in my opinion.

[DaveinOlyWA]

during Summer, i rarely hit the red bars. so i would say stick with the first 9 white bars.

[Stoaty]

There is some indication that it might be a good idea to avoid hitting turtle on a regular basis, but I doubt that anyone would want to do that.

Not true. I DO want to avoid hitting turtle on a regular basis.

[surfingslovak]

Not true. I DO want to avoid hitting turtle on a regular basis.

[Stoaty]

Wasn't there some Recent post regarding Tesla's long term storage strategy where the battery was kept at a very low SOC? Down at 1 bar remaining the cells are still at a relatively happy 3.6v which should still be fine for most types of driving. When you get really low (no miles/bars left) that's when things get hairy.. By the time the turtle comes on the cells have sunk to nearly 3.0v at which point drawing high current is probably not wise. Just resting at 3.2 or 3.3v I don't know though... Maybe it's not so bad(?). Even though the car for some reason doesn't enforce this, I would drive really mellow (ie just a few bubbles of power) if there are no more bars showing.

On the high side from what I understand stress on the battery is a function of high voltage and/or high temperature AND time. Ie reaching 4.1v (100%) isn't so bad as long as doesn't sit like that for many hours. So for example if you more or less leave the house at 8am every weekday morning, you could set the timer with no start time and an 8am end time at 100% and the pack would only be at 4.1v for a short time... That wouldn't leave much time for cell balancing (if it were needed) although that's a different topic.. Personally I find the lack of regen at 100% rather annoying. I don't know exactly how to measure stress on the cells.. For example I couldnt say if resting at 4.1v for an hour is better or worse than resting at 4.05v (80%) for 10 hours.. Or resting at 100 degrees for an hour was better or worse than sitting at 90 degrees for 10 hours... Or resting at a very low voltage(?)

Greg, do you have a list of the voltage at each number of bars showing? I would be interested in seeing a graph of this.

[mark13]

Well Im at 7000 miles now with all 100% charges ..The car salesman never said anything about 80% charges doing the 1 hour intro..Nissan also gave it to me with a 100% charge..

Next month I take it in for the 6 month check up...Ill see what they say about the 80% charge then..

Im still eyeing that 150 miles on a charge this winter in Phx..It was 101 today so it may not happen until Nov..

[LEAFfan]

Well Im at 7000 miles now with all 100% charges ..The car salesman never said anything about 80% charges doing the 1 hour intro..Nissan also gave it to me with a 100% charge..
Next month I take it in for the 6 month check up...Ill see what they say about the 80% charge then..
Im still eyeing that 150 miles on a charge this winter in Phx..It was 101 today so it may not happen until Nov..

6 month checkup? I thought the only thing at 7500 miles was a tire rotation? I've decided to wait a year for the battery pack check and go to Discount for a 'free' tire rotation since we're already a customer with the other car.
I'll be able to try that soon because I don't use A/C by myself. It will only take 7.2m/kWh. I've done 6.8 w/o A/C for shorter trips.