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Charging strategy for battery longevity

T34ME

Active Member
Mar 31, 2016
2,262
3,872
Inland Empire
I have a question about the best strategy for home charging to prolong the battery life. Let me start with some presumptions to simplify the scenario:
- for daily driving a max. of 80% charge
- for daily driving a min. of 20% charge
- presume I drive 20% of 100% charge everyday
Therefore I can drive for 3 days to deplete the battery from 80% to 20%

Is it better for battery health to charge everyday from 60% to 80%
or
Is it better for battery health to charge every third day from 20% to 80%
or
Does it matter?

My preferred strategy is to plug in at the end of every day, just to get into the habit (as I do now with my Prius Plug-In). I know that if I try to time it every third day, I will forget sometimes and wake up to a battery in need of a charge. :mad:
 
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mblakele

FSD Beta (99)
Mar 7, 2016
1,831
6,424
SF Bay Area
The manual recommends keeping the car plugged in as much as possible. So I'd give it an opportunity to charge every night, as long as it's reasonably convenient.

As I understand it the ideal cycle would center on 50%. So if you're using 20 percentage points a day, charge from 40% to 60% daily. But many people would get nervous with that cycle, and I think any benefits are marginal. Charging to 80% or 90% is probably fine too.

Based on behavior with recent Model S/X, I think you can expect about 5% degradation in the first year or two. I don't think charging habits will make a lot of difference there, as long as you avoid extremes like charging to 100% every day.
 
Completely agree with the previous response from mblakele. Ideally keep the mean charge around 50%, but more important just to stay away from the extremes for your usual charging. The only thing I would add is, as presumed by the OP, it is very easy to forget to plug in occassionally. Even if plugging in daily, I have owned a model s for 3 years and still sometimes do it. So if you charge to 60%, drive 20% charge worth that day and forget to plug in, you will probably be less than 40% after day 1 including vampire drain when not driving. Do the same the following day after forgetting to plug in and you might be in the mid teens by the time the overnight scheduled charge kicks in. I would keep my charge max cutoff further to the right to allow for more comfortably forgetting to plug in once in a while as is possible in this simple case short daily usage scenario. Also charge more to the right within reason to maybe allow for some travel beyond the norm occasionally.
 
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It really doesn’t make a difference, so don’t overthink it. Just set your daily charge limit and plug-in whenever you can.

wasn't there a survey a while ago which seemed to suggest that people who only charged the car to 70 or 80% got more degradation then those who did the "plug in and forget and leave max charge at default 92%" people?
 
My normal daily use on a P90D is about 38 Miles. And typical long distance spur of the moment is 120 miles.
So for me a 60% charge is about right and covers both the "norm" and the variant.
I plug in every day and have the S begin charging from my HPWC at 6 AM so the battery is warm by 7:30 departure.
So far this rate of charge and use have only given a 3% degradation since new (two years).
241 rated miles new at 90% and 235-6 rated now.
I do not deep cycle the battery near zero or to 100%. So therefore my pack is probably not "balanced", yet it is happy.
I do supercharge perhaps once or twice a month when coming back from a longer day's use but then only to 70% or so as to me 30 minutes sitting is a long time.... I listen to Leo Laporte the Tech Guy blog when supercharging. BTW Leo has an X.
 
Like everyone has mentioned, shallow cycling is better for lithium batteries although it may take a while for that difference to show up.

Most lithium batteries will lose capacity exponentially as a function of use, which results in less and less capacity loss over time. At some point (I've seen this referred to as a knee), capacity loss speeds up, the battery loses a lot of capacity in a short period of time, and it usually has to be replaced.

When the knee arrives seems to be a function of how deeply the batteries are discharged on average. The more they're discharged, the sooner the knee shows up and vice versa.
 

jdw

Member
Supporting Member
Jun 1, 2015
721
1,491
Vancouver
A good article on the topic and a graphic from it illustrating the general idea that shallow depth of discharge is better for lithium battery cycle life:

Screen Shot 2018-03-08 at 8.34.45 PM.png


These articles are not always 100% applicable to Tesla's, but there are some common sense ideas that seem to make sense - namely that SOC matters (use timed charging to keep the average SOC low), high power charging and hot batteries are not your friend (limit supercharging when you can and park in the shade :) and charge frequently to avoid deep discharge of the battery (a plugged in Tesla is a happy Tesla).
 
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mblakele

FSD Beta (99)
Mar 7, 2016
1,831
6,424
SF Bay Area
What section does it say that? I've been charging it to like 70% then leaving it unplugged until it gets down to ~20%. Sounds like I should just charge/top off to like 50% nightly?

Battery Information p138 (Model S — you tell me what the 3 manual says)

About the Battery
Model S has one of the most sophisticated battery systems in the world. The most important way to preserve the Battery is to LEAVE YOUR VEHICLE PLUGGED IN when you are not using it. This is particularly important if you are not planning to drive Model S for several weeks. When plugged in, Model S wakes up when needed to automatically maintain a charge level that maximizes the lifetime of the Battery.
There is no advantage to waiting until the Battery’s level is low before charging. In fact, the Battery performs best when charged regularly.​
 

TexasEV

Well-Known Member
Jun 5, 2013
7,656
8,935
Austin, TX
I recommend charging to 70% as often as possible. More than 70% and you start to get into the area where you get accelerated degradation just by having the car sit idle. The difference between 70% and 80% is admittedly small, though, so charging to 80% is almost as good.
This has not been the case with five years of the Model S, even for those of us who charge to 90%. Whatever theoretical difference there is, it’s not measurable.
 
In my X100D, I compromise at 75% (or ~220 miles).... In my head I think. I'm getting basically 100% of the range capacity of the X75D all the time when I leave my garage, with the power to go the full range when I need to in the event of road trips; all while prolonging my battery life.

When I get my LR model 3, I'll probably go around 71% or so (~220 miles); and think... I'm getting 100% range capacity of the SR model 3 all the time when I leave my garage, with the power to go the full 310 range when I need to on road trips; all while prolonging my battery life.
 

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