Does Running Battery Very Low Affect Capacity Over Time?

I have perused as many threads as I can find, but still can't find out whether running the battery down to 2 bars or 1 bar or Low Battery warning on a regular basis has any effect on battery capacity over time. In other words, should I try to avoid these low readings the same way I avoid charging over 80% (except when necessary)? I mention this in the context of my drive from West LA to Claremont, which I expect to make about 25 weekends per year. It took 7.5 bars at 50 MPH, but may take 9 bars at 60 MPH. I may not be patient enough to make the entire 100 mile round trip at a speed that low. In that case, will it be easier on the battery to cycle 10 bars to 1 bar, or 11 to 2 bars? I can charge as soon as I reach Claremont--probably on an L2 charger--so the downhill trip home won't take as much energy.

Stoaty said:

be easier on the battery to cycle 10 bars to 1 bar, or 11 to 2 bars?

Click to expand...

I don't think we know that answer, but I use the 10 to 1 method, since it's easier to charge to 80%, and there's less battery heating than charging to 90%.

Those 2 choices have come up before and much speculation ensued.

One point brought up, to keep in mind, is that the bottom two bars tend to be "beefier" with recent firmware so that people are less inclined to run out. A bigger 'reserve tank' so to speak. So, I would tend to go with the 10 to 1 (instead of 11 to 2) approach. Also, as was just said, it is a lot easier to stop at 80% than 90%.

On the flip side, some say it is better to add a little extra 'just in case', so if something unforeseen happens you still make it to a charging spot. Planning to run down to your last bar puts you at risk of totally running out if something unexpected happens.

TEG said:

On the flip side, some say it is better to add a little extra 'just in case', so if something unforeseen happens you still make it to a charging spot. Planning to run down to your last bar puts you a risk of totally running out if something unexpected happens.

Click to expand...

That won't be a problem, since I am going out there specifically to hike in the Mount Baldy area. The plan is to leave my Leaf to charge, and ride up to Baldy with my brother who will be coming from Redlands in his ICE car. Thanks for both replies. I think I will stick with the 10 bars -> 1 bar (or 2 bars, depending on how fast I drive) since it is easier to charge to 80%. Presumably Nissan has left enough forbidden charge area on the bottom to prevent harm to the battery.

Stoaty said:

but still can't find out whether running the battery down to 2 bars or 1 bar or Low Battery warning on a regular basis has any effect on battery capacity over time.

Click to expand...

Nissan has never said, but they have talked about the 80% long life mode and the warning about too many quick charges. Operating a battery on the lower extremes of charge does increase the heat. It will be interesting when we can get a true temperature reading using the Can-bus.

I suspect that Nissan hides a safety reserve of 11% when the car shuts down in turtle mode.

Stoaty said:

TEG said:

...going out there specifically to hike in the Mount Baldy area...

Click to expand...

Click to expand...

I have spent a great deal of time going up that hill in all kinds of weather, from the village, manker flats to hut trail or the devils backbone, and and even cross countried up an area known as "Good Canyon" named after an old fire chief. By the way, Good Canyon is very rugged, but can be used to access some areas that hold snow for late season backcountry skiing, but also there is plenty of rockfall hazard and other things that go along with being off the main tracks.

My own plan is to top off at the SCE charge in Irwinidale, and drive the LEAF for the whole deal from Santa Monica area. I think I will only need to charge once on the way up but we will see....

Back on topic, I have read in several places in the forum that the empty turtle mode still maintains a margin of charge in the battery and that going down to one keeps it in the reasonable range of battery function.

My own approach, based on "numerology" without a shred of scientific evidence, is to say if 80% is a comfortably safe top, then 20% is a comfortably safe bottom. Tony's chart says 80% = ~9.5 bars and 20% = ~0.5 bars. There's your 9-bar range, so charge to 80%.

I'm willing to go to 100% occasionally, and down into LBW or VLBW occasionally, while avoiding both extremes as a routine. But one bar? No sweat.

Ray

My approach is to charge to 80% whenever I can. I wouldn't charge higher just to avoid the lower two bars for battery life purposes, although I would do so to improve my flexibility (and avoid range anxiety). My view is that if you need to go down there, go ahead...if you have a chance to add charge (especially up to 80%) and avoid those bars, good.

I agree with others that charging to 80% in your case would be better for battery life. There seems to be more "padding" below the bottom end of the allowable charge range than above the top end.

Stoaty said:

... I am going out there specifically to hike in the Mount Baldy area. The plan is to leave my Leaf to charge, and ride up to Baldy with my brother who will be coming from Redlands in his ICE car.

Click to expand...

Just a thought, but could you stay overnight in Claremont the night before, charge the LEAF, and ride up to Baldy in the LEAF? I don't think you'd have a problem getting up to the top of Baldy road on an 80% charge from Claremont.

abasile said:

Just a thought, but could you stay overnight in Claremont the night before, charge the LEAF, and ride up to Baldy in the LEAF? I don't think you'd have a problem getting up to the top of Baldy road on an 80% charge from Claremont.

Click to expand...

It might have worked out this weekend, but generally one of my other brothers will ride with me from WLA, and he has to work Friday and wouldn't be amenable to driving out Friday evening (nor would I).

abasile said:

I agree with others that charging to 80% in your case would be better for battery life. There seems to be more "padding" below the bottom end of the allowable charge range than above the top end.

Stoaty said:

... I am going out there specifically to hike in the Mount Baldy area. The plan is to leave my Leaf to charge, and ride up to Baldy with my brother who will be coming from Redlands in his ICE car.

Click to expand...

Just a thought, but could you stay overnight in Claremont the night before, charge the LEAF, and ride up to Baldy in the LEAF? I don't think you'd have a problem getting up to the top of Baldy road on an 80% charge from Claremont.

Click to expand...

I think it will use about 6-7 bars based on mileage and elevation from SGE in Irwindale. That might mean a couple of hours in charge or less from arrive to moving on.

JimSouCal said:

abasile said:

Just a thought, but could you stay overnight in Claremont the night before, charge the LEAF, and ride up to Baldy in the LEAF? I don't think you'd have a problem getting up to the top of Baldy road on an 80% charge from Claremont.

Click to expand...

I think it will use about 6-7 bars based on mileage and elevation from SGE in Irwindale. That might mean a couple of hours in charge or less from arrive to moving on.

Click to expand...

My guess, based on experience with our climb up CA-330, would be 7 bars from Claremont to the Mt. Baldy Ski Lifts. Another 2-3 bars from SCE in Irwindale.

Stoaty said:

but still can't find out whether running the battery down to 2 bars or 1 bar or Low Battery warning on a regular basis has any effect on battery capacity over time.

Click to expand...

Herm said:

Operating a battery on the lower extremes of charge does increase the heat.

Click to expand...

Why is that? What's different about discharging when the battery is full, half empty, or near empty?

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(?)

GregH said:

Wasn't there some Recent post regarding Tesla's long term storage strategy where the battery was kept at a very low SOC?

Click to expand...

You are referring to the info at this link:

http://www.teslamotorsclub.com/showthread.php/3848-Tesla-Roadster-Battery-Care" onclick="window.open(this.href);return false;

"When plugging in a nearly empty car that is set to Storage mode, the charge will generally stop at around 20%. The car will then settle into its normal Storage mode rhythm, topping up and discharging between 10% and 50% as the car sees fit. Oftentimes it will keep a tighter envelope based on parameters that I am not aware of.

Most important to remember is that Storage mode is not intended to be a driving mode. This charge setting is primarily meant to optimize battery life while the car is under storage conditions for two weeks or more."

Stoaty said:

http://www.teslamotorsclub.com/showthread.php/3848-Tesla-Roadster-Battery-Care" onclick="window.open(this.href);return false;

"When plugging in a nearly empty car that is set to Storage mode, the charge will generally stop at around 20%. The car will then settle into its normal Storage mode rhythm, topping up and discharging between 10% and 50% as the car sees fit. Oftentimes it will keep a tighter envelope based on parameters that I am not aware of."

Click to expand...

Tesla owners have the best battery management knowledge and control, but dont forget they have active temperature control while plugged-in and a far more volatile chemistry. Leaf owners would also benefit from those procedures.

Lately, during the hours our LEAF is not in use, I try to leave the state of charge between three and seven bars. If the SOC is less than two full bars, I charge immediately. If a higher state of charge is needed to drive somewhere, I manually charge it to eight bars. Keeping the time-averaged SOC lower should be a little better for battery longevity.

As I've mentioned before, on most days the charging timers are useless for us. Living on a mountain, I find that charging to 80% is higher than ideal for any trip that involves significant downhill. Even for drives to Lake Arrowhead or Crestline, which are 1000 and 1500 feet lower than us, respectively, we find that we can maximize continuous regen on the steeper downhills only by limiting the starting SOC to eight bars. For trips all the way down the mountain (5000 foot descent), starting with seven or fewer bars is better. On our most recent descent, we went from seven full bars to barely ten bars. That's getting closer to "fast charging" territory. As I know that our heavy use of regen puts more stress on the battery (more stress than climbing the mountain), I am motivated to do whatever else I can to treat it gently.

abasile said:

As I know that our heavy use of regen puts more stress on the battery (more stress than climbing the mountain), I am motivated to do whatever else I can to treat it gently.

Click to expand...

So, use the brakes! There's a punch line from back in the ICE days. After a few pages of discussions like this (usually about engine braking), someone will point out (and I paraphrase here), "Batteries cost $15,000. Brake pads cost $25!"

Really, I understand what you're doing here. I just think we should work out our favorite ways, and be happy with them. It's going to be all right in the end.

aqn said:

Herm said:

Operating a battery on the lower extremes of charge does increase the heat.

Click to expand...

Why is that? What's different about discharging when the battery is full, half empty, or near empty?

Click to expand...

The internal resistance is higher. Though I can't recall ever hearing that that is significant enough to include in our incessant worrying

gbarry42 said:

aqn said:

Herm said:

Operating a battery on the lower extremes of charge does increase the heat.

Click to expand...

Why is that? What's different about discharging when the battery is full, half empty, or near empty?

Click to expand...

The internal resistance is higher. Though I can't recall ever hearing that that is significant enough to include in our incessant worrying

Click to expand...

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.