Worst-case Scenario Range Estimates for each battery type (my calculations)

[JoeUser]

I'm not sure why you have the lower limit at 20%... While it is true that EVs do not like to be stored below 20%, there is no issue with driving them below that number. I have no qualms arriving somewhere with 2% if there is a charger there. And while it is good practice not to leave an NMC battery above 80% if you don't need to, if you need more range there it's totally fine to charge to 100%. Some EVs even until very recently didn't have an option to set a charge limit, they are charged to 100% every day.

There is also some confusion about what 100% actually means. 4.2V is what cell manufacturers calls 'safe' 100%, but the carmaker calls 100% is normally below that number to preserve battery longevity (hence the 'gross capacity' and 'usable capacity' numbers you see sometimes). So academic studies on cell longevity cannot be directly applied to what you see on your screen.

I've been an EV mechanic for a long time, and my advise to people is to not stress about the battery. The OEM has done their homework, they are not going to let you do serious damage. I've seen babied packs fail at 40k, and I've seen uber-driver 100% daily packs just fine at 250k. Every study on EV batteries just shows that they are tougher and more resilient than we expected, and those studies are on old pack designs. New packs are much, much better.

 

[KevinRS]

I'm not sure why you have the lower limit at 20%... While it is true that EVs do not like to be stored below 20%, there is no issue with driving them below that number. I have no qualms arriving somewhere with 2% if there is a charger there. And while it is good practice not to leave an NMC battery above 80% if you don't need to, if you need more range there it's totally fine to charge to 100%. Some EVs even until very recently didn't have an option to set a charge limit, they are charged to 100% every day.

There is also some confusion about what 100% actually means. 4.2V is what cell manufacturers calls 'safe' 100%, but the carmaker calls 100% is normally below that number to preserve battery longevity (hence the 'gross capacity' and 'usable capacity' numbers you see sometimes). So academic studies on cell longevity cannot be directly applied to what you see on your screen.

I've been an EV mechanic for a long time, and my advise to people is to not stress about the battery. The OEM has done their homework, they are not going to let you do serious damage. I've seen babied packs fail at 40k, and I've seen uber-driver 100% daily packs just fine at 250k. Every study on EV batteries just shows that they are tougher and more resilient than we expected, and those studies are on old pack designs. New packs are much, much better.

Exactly. There is a lot of 3rd party and self upselling going on with range. Manufacturers build considerations like that 80/20 and just what type of cells they are using into their charge controllers and range estimates. Just as cell phone manufacturers are more recently limiting max charge and adjusting battery level indications for more longevity.
The 80/20 recommendation comes from when you'd have complete control and see where you are relative to the actual MAX charge and truly dead flat. Like if you were putting together a battery system for your house, and building it from cells, and programming the controller by the voltages of the cells.

Now with people worried about range, they end up with hybrids with smaller batteries and a gas tank, and never touch the gas until they decide they need to run the battery down to use the gas so it doesn't go bad. Same with BEVs buy 300+ miles of range, and drive 50 or less a day.

 

[Lynx]

I'm not sure why you have the lower limit at 20%... While it is true that EVs do not like to be stored below 20%, there is no issue with driving them below that number. I have no qualms arriving somewhere with 2% if there is a charger there. And while it is good practice not to leave an NMC battery above 80% if you don't need to, if you need more range there it's totally fine to charge to 100%. Some EVs even until very recently didn't have an option to set a charge limit, they are charged to 100% every day.

The thought process behind having 20% as a lower bound is based on the evidence that depth of discharge affects battery longevity.

Starting at 4:32 to 8:30, this youtube video explains why discharging at an excessive depth is bad for NMC batteries at a chemical level due to NMC electrode particles cracking, and it includes a study showing this result:


Therefore, in an ideal world keeping the battery between 80/20% just reduces the range of discharge to 60% of the overall capacity, which should mean that the battery should theoretically suffer 40% less damage from discharging over time than if you had a constant 100/0% range of discharge, and it would suffer 20% less damage then if you went from 80/0% range of discharge.

For the purpose of my thought experiment, I just picked 80/20% (60% range of discharge) as a general rule-of-thumb for someone who really wants to prolong their battery longevity in a worst-case scenario. But of course everyone's situation is unique and subjective so this could easily be altered for anyone who is fine with a greater depth of discharge.

 

[E90400K]

I'm not sure why you have the lower limit at 20%... While it is true that EVs do not like to be stored below 20%, there is no issue with driving them below that number. I have no qualms arriving somewhere with 2% if there is a charger there. And while it is good practice not to leave an NMC battery above 80% if you don't need to, if you need more range there it's totally fine to charge to 100%. Some EVs even until very recently didn't have an option to set a charge limit, they are charged to 100% every day.

There is also some confusion about what 100% actually means. 4.2V is what cell manufacturers calls 'safe' 100%, but the carmaker calls 100% is normally below that number to preserve battery longevity (hence the 'gross capacity' and 'usable capacity' numbers you see sometimes). So academic studies on cell longevity cannot be directly applied to what you see on your screen.

I've been an EV mechanic for a long time, and my advice to people is to not stress about the battery. The OEM has done their homework; they are not going to let you do serious damage. I've seen babied packs fail at 40k, and I've seen uber-driver 100% daily packs just fine at 250k. Every study on EV batteries just shows that they are tougher and more resilient than we expected, and those studies are on old pack designs. New packs are much, much better.

Good post.

I think some of the perception issue is EPA range estimates tied to state of charge level. Meaning, if the EPA max range is 240 miles at 100% (useable) battery capacity depletion yet manufacturers state in their owner's manual to charge only to 80% and deplete only to 10% (worst case), for road trips that drastically reduces range for those who are contemplating their first EV purchase. Reading internet EV forums for several years now the issue of charging etiquette arises regarding charging past 80% as the charge speed curve significantly drops from 80% to 100%.

More significant is winter range. The EPA gives zero insight as to range relative to ambient temperature. Manufacturers give no information as to real impact of cold weather on both range and recharge speed. As a consumer I think the EPA range estimates should include specific impacts of cold weather operation on both range and recharge speed. It is difficult to ask of buyers considering their first EV purchase to take such a significant financial risk as the purchase of an EV only to discover it does not fit their intended use case. It's fine to think in terms of averages and 50 miles per day when the EV has a theoretical (tested?) range of 240 miles, but such averages are too simplistic in my opinion to make such a significant financial decision.

As a consumer using the Maroney window sticker as part of the purchase decision, my experience with the last seven ICEV I have purchased, all have achieved significantly better fuel consumption results than the numbers predicted from the EPA testing. I believe it is fair to say EV EPA estimates are mostly optimistic for EV range predictions. Add in cold weather operation and the EPA numbers are even more useless.

 

[KevinRS]

I think part of the problem with cold weather estimates is it can vary a lot. Vehicle stored in relatively warm garage, and precondition battery and passenger compartment before unplugging, you will go a lot farther than if parked on the street or a driveway in sub-freezing weather and start cold.
Any reasonable "cold weather" test regime to come up with a range can be blown away by driving habits, blasting the heater, etc.
Not to mention: How cold is cold? My cold only rarely gets below freezing anymore, though 30+ years ago we had weeks at a time below freezing occasionally here. For some cold is -40 or lower, in which case of course you are going to precondition, just as with an ICEV you'd use a block heater.

 

[AZFox]

One other thing to note is that if you preheat the cabin before leaving while still plugged in, the range difference is much lower. It's much easier to maintain a cabin's temp than it is to make the big sweeping change when you first get in and try to bring it up to temp. This is why many people are hoping that the Slate's fob will support preheating from the "2X" button.

Count me among those many people. For me it's important for cooling in Summer as well as heating in Winter.

 

[KevinRS]

In winter, when leaving for work early, starting up the heat a few minutes before leaving would be great, especially when it gets cold enough for frost, and in the summer, that's when more range than a regular fob would be good, to start up the AC when clocking out of work.