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Is it ok to charge Tesla Model 3 only once or twice a week?
- Thread starter snoopydeal
- Start date
This would be worse for the battery compared to charging daily. Check out this chart that I found here. The top three lines (orange, purple and light-blue) show 75-65%, 75-45% and 75-25%. That means instead of following the orange line, your degradation will follow the light-blue line.
However, the cycles shown here are too high. Instead of looking at the lines at 5000 cycles, you need to compare them at 500 cycles. Assuming you get 220 miles real world range in SR+, 500 cycles would be 110,000 miles and would probably cover your entire ownership duration as a low mileage driver.
The difference between orange and light-blue lines looks like 98.5% vs 96% around 500 cycles. In other words, if you continue this way, at 110,000 miles your SR+ with 240 miles range will likely have 0.96*240= 230 miles rated range left compared to 0.985*240= 236 miles if you were to charge daily.
Some people might say, 96.5% at 110,000 miles is too much degradation because Tesla's battery packs have liquid cooling. Yes, but this test was done at 20°C (68°F). Also, check out the chart here that shows 93% average capacity for Model S/X at 110,000 mi. Model 3 battery is more advanced than S/X. Therefore it should have more capacity left than 93%. Therefore 98.5% or 96% would be completely normal for Model 3 at 110,000 mi.
However, the cycles shown here are too high. Instead of looking at the lines at 5000 cycles, you need to compare them at 500 cycles. Assuming you get 220 miles real world range in SR+, 500 cycles would be 110,000 miles and would probably cover your entire ownership duration as a low mileage driver.
The difference between orange and light-blue lines looks like 98.5% vs 96% around 500 cycles. In other words, if you continue this way, at 110,000 miles your SR+ with 240 miles range will likely have 0.96*240= 230 miles rated range left compared to 0.985*240= 236 miles if you were to charge daily.
Some people might say, 96.5% at 110,000 miles is too much degradation because Tesla's battery packs have liquid cooling. Yes, but this test was done at 20°C (68°F). Also, check out the chart here that shows 93% average capacity for Model S/X at 110,000 mi. Model 3 battery is more advanced than S/X. Therefore it should have more capacity left than 93%. Therefore 98.5% or 96% would be completely normal for Model 3 at 110,000 mi.
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patrick80132
Member
So am I reading this right that maintaining a daily overnight charge to between 75-65% would be ideal for say maybe someone doing 40 miles a day or so?
golfpilot
Member
Lot of info missing from that chart. It says 68 degrees but what does that even mean? Are they actively being cooled to 68 degrees or are the batteries just laying on a table in a 68 degree room? Tesla batteries also have 5-6 kwh unusable. That can be 6-10% of your battery. That is likely why elon says charge to 90% and leave it plugged in. At "90%" the car is closer to the 80% number and you want to stay plugged in because it allows the car smaller tolerances. If I leave my car at 90% for 10 days but plugged in, the car will slowly deplete the charge to maintain the battery. If it gets real low it will bump up a little. My Rav4 doesn't manage the battery like this. Since I only drive it once every 2 weeks or so I leave it unplugged at 50% SOC (and that is an early Tesla battery)
Point is, the new Tesla BMS is very smart and comparing your car to a battery test where they laid batteries out in a room temperature room and started charging and discharging is not a fair comparison. Plug your car in when you can for as long as you can, charge to 90% most of the time and 100% when you need it, and enjoy your car.
If you can only plug in once or twice a week thats fine, but beware that the car may lose a significant amount of charge while sitting there not plugged in if the BMS needs to cool/heat something.
Point is, the new Tesla BMS is very smart and comparing your car to a battery test where they laid batteries out in a room temperature room and started charging and discharging is not a fair comparison. Plug your car in when you can for as long as you can, charge to 90% most of the time and 100% when you need it, and enjoy your car.
If you can only plug in once or twice a week thats fine, but beware that the car may lose a significant amount of charge while sitting there not plugged in if the BMS needs to cool/heat something.
The problem with that Dynamic Stress Test chart is that it's equating all cycles (e.g. comparing 500 cycles of 100% - 25% and 500 cycles of 75% - 65%).
However, drawing down a Model 3 battery from 100% to 25% is about 56 kWh, or driving 225 miles.
And only discharging from 75% to 65% represents 7.5 kWh, or driving 30 miles.
So telling me that 75% - 65% is better than 100% - 25% doesn't really tell me anything, right? Because the Dynamic Stress Testing is telling me that cycling the battery less is better. Well, no *sugar*.
The problem is, we don't really have a choice of changing the amount of energy we require from the battery in our car. We're just talking about charging patterns; whether discharging from 80%-70% 3 times a week is better or worse than discharging from 80%-50% once a week.
I'm inclined to think that the best thing you can do for the battery's health is keep its average closer to 50% (i.e., charge once a week, since that means the battery spends more time at a lower State of Charge, closer to 50%). I'm basing this off of another Battery University claim on charge voltage limit.
This is more compelling to me, as even if they are comparing unequal discharge energy amounts, 10% reduction in available energy doubles discharge cycles. So I tend to lower charge limit as is still convenient (70/80%), and charge when I get down to 50%.
But it's important to note that the Model 3 manual says to keep it plugged in all the time. So this could all be meaningless. I don't know. If I've gotten something wrong, please correct me.
However, drawing down a Model 3 battery from 100% to 25% is about 56 kWh, or driving 225 miles.
And only discharging from 75% to 65% represents 7.5 kWh, or driving 30 miles.
So telling me that 75% - 65% is better than 100% - 25% doesn't really tell me anything, right? Because the Dynamic Stress Testing is telling me that cycling the battery less is better. Well, no *sugar*.
The problem is, we don't really have a choice of changing the amount of energy we require from the battery in our car. We're just talking about charging patterns; whether discharging from 80%-70% 3 times a week is better or worse than discharging from 80%-50% once a week.
I'm inclined to think that the best thing you can do for the battery's health is keep its average closer to 50% (i.e., charge once a week, since that means the battery spends more time at a lower State of Charge, closer to 50%). I'm basing this off of another Battery University claim on charge voltage limit.
This is more compelling to me, as even if they are comparing unequal discharge energy amounts, 10% reduction in available energy doubles discharge cycles. So I tend to lower charge limit as is still convenient (70/80%), and charge when I get down to 50%.
But it's important to note that the Model 3 manual says to keep it plugged in all the time. So this could all be meaningless. I don't know. If I've gotten something wrong, please correct me.
timk225
Active Member
I charge to 90% and only plug in when the car needs it, which is usually in the 20%-30% range, sometimes more, sometimes less.
I was looking into charging at work. I walked all around the buildings looking for places I could plug in, and the best I could do is plug into a 5-20 outlet. Still, that would more or less cover my daily needs during the work week if it has 10-12 hours charging on a 5-20 while I'm at work. My days are mostly 10-12 hour shifts.
But when I asked the boss man on Monday, he said "Mmmmmmmmmm...... I know it's good to support EVs, but..... nah". He claimed the managers are on him to keep the power usage down, never mind the fact that this business uses a huge amount of power as its normal mode of operation, and even if I could charge on a 14-50 it would hardly be noticeable.
I was looking into charging at work. I walked all around the buildings looking for places I could plug in, and the best I could do is plug into a 5-20 outlet. Still, that would more or less cover my daily needs during the work week if it has 10-12 hours charging on a 5-20 while I'm at work. My days are mostly 10-12 hour shifts.
But when I asked the boss man on Monday, he said "Mmmmmmmmmm...... I know it's good to support EVs, but..... nah". He claimed the managers are on him to keep the power usage down, never mind the fact that this business uses a huge amount of power as its normal mode of operation, and even if I could charge on a 14-50 it would hardly be noticeable.
If you are charging 75-65, that's only 10% per each charge. If you are charging 85-25, that's 60% per each charge. So one 85-25 cycle equals to 6 75-65 cycles in terms of your mileage.
In other words, if you charge 85-25, that's 60% of 300, or 180 miles per charge. You can do it 2000 times (360,000 miles) before battery capacity drops to 90%.
If you charge 75-65, that's 30 miles per charge. You can do it 9000 times (180,000 miles) before it drops to 90%.
Charging 85-25 is better in the long run.
Aside from the math differences, don't get confused on charging sessions versus charging cycles.
Charging cycles derives pretty closely from the total miles driven, because one cycle is one full battery capacity removed and then refilled. Whether you empty it all at once and recharge once, or whether you drain and refill a fourth of it four times, or whether you drain one tenth of it and refill that ten times, those are all still one cycle, just done in many different numbers of charge sessions.
So obviously how you do those cycles does affect the battery--whether the charging sessions are short or long, whether it's near the top or the middle of the battery %, what temperature it's at, etc.
Charging cycles derives pretty closely from the total miles driven, because one cycle is one full battery capacity removed and then refilled. Whether you empty it all at once and recharge once, or whether you drain and refill a fourth of it four times, or whether you drain one tenth of it and refill that ten times, those are all still one cycle, just done in many different numbers of charge sessions.
So obviously how you do those cycles does affect the battery--whether the charging sessions are short or long, whether it's near the top or the middle of the battery %, what temperature it's at, etc.
From what I can gather; I don't do much driving either as I work from home. But a plug in Tesla is a happy Tesla. Also I charge to 90 percent as Elon as mentioned and other on the board that has longer ownership. I figured 8 years warranty on battery; something goes wrong I get a new battery with new technology in a few years.
Arizona Willie
Member
I'm retired and don't drive a lot either.
I charge to 90% and then disconnect and don't charge again until the range is down to about 100 miles.
I just charge from a 120 volt outlet in the carport. I'm in no hurry.
It's the number of charge cycles that matter, not the number of charge sessions. The chart in message #3 shows cycles. 1 cycle is when the percentages of multiple sessions add up to 100%. Charging 10 times from 65% to 75% (10x10%) or 2 times from 25% to 75% (2x50%) are both 1 cycle. The idea that the first option must be worse because 10 sessions are a lot more than 2 sessions, is wrong. In both scenarios, you get 1 cycle.
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Nope. The chart shows 75-65 sessions. The chart has an explanation. 75-25% provides the most energy.
https://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries
Case 1: 75–65% SoC offers longest cycle life but delivers only 90,000 energy units (EU). Utilizes 10% of battery.
Case 2: 75–25% SoC has 3,000 cycles (to 90% capacity) and delivers 150,000 EU. Utilizes 50% of battery. (EV battery, new.)
Case 3: 85–25% SoC has 2,000 cycles. Delivers 120,000 EU. Uses 60% of battery.
Case 4: 100–25% SoC; long runtime with 75% use of battery. Has short life. (Mobile phone, drone, etc.)
This is a VERY misleading chart, and the poster has drawn some invalid conclusions because it is so confusing (not blaming him, it's easy to mis-read the chart).
Let's consider just the ORANGE line for a moment. At 1000 cycles, the battery shows about 96% capacity. So the conclusion might appear that if you follow the orange charge/discharge model, you will have 96% battery capacity at 1000x220 miles, or about 200,000 miles, assuming you have a battery capacity of 220 miles (as per the last post).
The trouble is, the math is wrong. The orange line represents a 75-65% charge discipline. That is, you charge to 75% and recharge at 65%. BUT this of course is only 10% of battery capacity, which mean you drive only 10% of battery capacity between charges. So you only drive 10% x 220 miles, or 22 miles between each charge. So those 1000 charge cycles occur after you have driven 1000 x 22 miles, which is only 22,000 miles.
Now look at the BLUE line. At 1000 cycles, the battery is at about 93%. The blue line represents a 75-25% charge discipline, which is 50% of battery capacity. This means, you have driven 50% x 220 x 1000 miles, or 110,000 miles.
So when you read the graph, the orange and blue lines at 1000 DST cycles represent DIFFERENT miles driven. The orange line is 22,000 miles while the blue line is 110,000 miles. You can't really draw any conclusions from the chart without adjusting for miles driven.
In fact, the orange line will only reach 110,000 miles driven after 5000 DST cycles, and if you look at the chart the orange line is ALSO at about 93% at 5000 cycles (I'm baffled by that spike, but lets ignore that).
So, in actual fact, what the chart is saying is the the ORANGE and BLUE charge disciples yield about the same results when comparing battery capacity after driving the same number of miles. This is not what a casual glance at the chart suggests, which is why its really a misleading chart. To be useful, the x-axis of the chart should show miles driven, not DST cycle count.
Treetop235
Member
My round trip is about 25 to 30 miles. I charge to 75% each night, and use STATS to Smart Prep my battery to 80% 30 minutes before I leave for work.
Elon states that keeping the car plugged in is best as the computer will manage the battery for maximum life and best performance.
If I am going on a trip, then I will go 90% to 100%.
This is all home charging using a wall charger, 48Amps max.
@Dan123, it turns out the chart I posted is misleading. On the same page, this other chart is better. As you can see, at the same number of cycles (meaning at the same mileage), 75-25% is better than 85-25%.
Also, there is another chart I found here. Again, it shows it's better to keep the depth of discharge (DOD) low. In other words, 90-80% (10% DOD) is better than 90-60% (30% DOD). Therefore it would be better if OP charged daily instead of once or twice a week.
The owner's manual suggests the same thing. This is from page 122 here.
I don't think this is going to make a huge difference. At 100,000 miles, OP might see 3% more degradation compared to charging daily.
Also, there is another chart I found here. Again, it shows it's better to keep the depth of discharge (DOD) low. In other words, 90-80% (10% DOD) is better than 90-60% (30% DOD). Therefore it would be better if OP charged daily instead of once or twice a week.
The owner's manual suggests the same thing. This is from page 122 here.
I don't think this is going to make a huge difference. At 100,000 miles, OP might see 3% more degradation compared to charging daily.
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By the way, here are the links to the Tesla battery survey:
- Step 1: Google form to enter your range at 100%. Open the same form and click 'Edit your response' to add more entries.
- Step 2: Google Sheet to compare your capacity to other entries. Select your username on the 'Charts' tab.
That's a really cool product, Troy. Now I'm trying to justify spending $1200, haha.
However, I wish that second chart were more descriptive. I think a 10% Depth of Discharge implies starting at 100% and discharging to 90%... but they don't specify the actual beginning percentage and ending percentage. It would be really useful to know the starting percentage. Because I'd be really surprised if 10% Depth of Discharge, starting at 100%, resulted in the longest cycle life. The battery's then spending lots of time near 100%, and I've been under the impression that that's the most stress you can place on Lithium Ion batteries.
However, I wish that second chart were more descriptive. I think a 10% Depth of Discharge implies starting at 100% and discharging to 90%... but they don't specify the actual beginning percentage and ending percentage. It would be really useful to know the starting percentage. Because I'd be really surprised if 10% Depth of Discharge, starting at 100%, resulted in the longest cycle life. The battery's then spending lots of time near 100%, and I've been under the impression that that's the most stress you can place on Lithium Ion batteries.
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