Why is it bad to charge to 100% (Nominal/Usable)

[Timberlake]

I may have this all wrong, but If I'm not mistaken, all EV batteries have nominal battery size and a usable battery size. Wouldn't that mean charging to "100%" is really only charging to 90% or whatever is actually usable, keeping the battery healthy?

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[Maquis]

There’s a guy on the Lightning forum that tests batteries for a living. He says he can see much higher levels of degradation if you repeatedly charge cells beyond 80% of total capacity. He routinely charges to 85% indicated SoC, which roughly corresponds to that 80% figure. He’s not afraid to charge higher when he needs it, but if you want to maximize battery health, don’t charge above 85% if you don’t need to.

 

[hybrid2bev]

This is why we can’t have nice things, buffer.

 

[Mach-Lee]

I may have this all wrong, but If I'm not mistaken, all EV batteries have nominal battery size and a usable battery size. Wouldn't that mean charging to "100%" is really only charging to 90% or whatever is actually usable, keeping the battery healthy?

Note, this advice applies to the NCM chemistry batteries only (not LFP).

Fully charging the cells produces the highest cell voltage, which induces side reactions that can damage the battery and cause capacity loss. You want to minimize the amount of time the battery pack is at 100% so these damaging side reactions are minimized (voltage drives reactions). It is okay to be at 100% for a few hours, but you don't want to leave it like that for days.

To make a simple analogy, think of it like high blood pressure. It's okay to be at a high blood pressure for short time (such as during exercise), but having chronic high blood pressure that goes on all day and night is damaging to your body.

I will second the advice to keep the pack under 85% when possible. That's a low enough voltage not to cause excessive degradation.

 

[JohnFoxeSheets]

Note, this advice applies to the NCM chemistry batteries only (not LFP).

Fully charging the cells produces the highest cell voltage, which induces side reactions that can damage the battery and cause capacity loss. You want to minimize the amount of time the battery pack is at 100% so these damaging side reactions are minimized (voltage drives reactions). It is okay to be at 100% for a few hours, but you don't want to leave it like that for days.

To make a simple analogy, think of it like high blood pressure. It's okay to be at a high blood pressure for short time (such as during exercise), but having chronic high blood pressure that goes on all day and night is damaging to your body.

I will second the advice to keep the pack under 85% when possible. That's a low enough voltage not to cause excessive degradation.

It's interesting that Ford still recommends 90% rather than lower. (I know it's a balance between the need for range vs. the need for long term battery capacity...)

 

[Mach-Lee]

It's interesting that Ford still recommends 90% rather than lower. (I know it's a balance between the need for range vs. the need for long term battery capacity...)

90% is still above 4.0V/cell (about 4.04V), us battery nerd types like to keep it below that value. 90% will get you through the 8 year warranty period, but if you want it to last a lot longer, lower is better. If you want max life, charge it to 70% or less daily.

My personal rule is don't let it stay above 85% for more than 12 hours.

 

[JohnFoxeSheets]

90% is still above 4.0V/cell (about 4.04V), us battery nerd types like to keep it below that value. 90% will get you through the 8 year warranty period, but if you want it to last a lot longer, lower is better. If you want max life, charge it to 70% or less daily.

My personal rule is don't let it stay above 85% for more than 12 hours.

Thanks!

 

[hprose]

It's interesting that Ford still recommends 90% rather than lower. (I know it's a balance between the need for range vs. the need for long term battery capacity...)

Ford recommends 80. They changed it long ago. BTW Apple recommends 80 for the iPhone.

 

[generaltso]

Ford recommends 80. They changed it long ago.

No, they don’t. And no, they didn’t.

The 80% recommendation only applies to DCFC and is because of time (and cost in some cases).

 

[Trigger]

Charging at Home (Level 1 & 2 AC Charging)

• Lithium Iron Phosphate (LFP) batteries: Set the maximum charge level to 100%. Charge to 100% at least once per month to maintain estimated in-vehicle range accuracy (both state of charge and distance to empty). If not charged to 100% at least once per month, owners may experience degraded vehicle performance and a decrease in the accuracy of the vehicle's estimated range.
• Nickel Cobalt Manganese (NCM) batteries: Set the maximum charge level to 90% to reduce strain on the battery. Setting the maximum charge level to 100% provides full range for long trips.

DC Fast Charging On-the-Road
Charging your LFP or NCM battery to 80% minimizes your time charging and reduces battery capacity degradation (since charging rates will slow between 80-100%).

https://www.ford.com/support/how-to... (LFP) batteries,charge and distance to empty).

 

[JohnFoxeSheets]

Ford recommends 80. They changed it long ago. BTW Apple recommends 80 for the iPhone.

If you click the link in my comment you’ll see that they recommend 90%.

 

[mdolan92869]

Charging at Home (Level 1 & 2 AC Charging)

• Lithium Iron Phosphate (LFP) batteries: Set the maximum charge level to 100%. Charge to 100% at least once per month to maintain estimated in-vehicle range accuracy (both state of charge and distance to empty). If not charged to 100% at least once per month, owners may experience degraded vehicle performance and a decrease in the accuracy of the vehicle's estimated range.
• Nickel Cobalt Manganese (NCM) batteries: Set the maximum charge level to 90% to reduce strain on the battery. Setting the maximum charge level to 100% provides full range for long trips.

DC Fast Charging On-the-Road
Charging your LFP or NCM battery to 80% minimizes your time charging and reduces battery capacity degradation (since charging rates will slow between 80-100%).

https://www.ford.com/support/how-tos/electric-vehicles/home-charging/how-do-i-maintain-my-electric-vehicle-battery/#:~:text=Lithium Iron Phosphate (LFP) batteries,charge and distance to empty).

If you keep supplying documentation supporting your stance and actually citing the source, you're going to get kicked off the internet. ?

 

[mbelcik]

Charging at Home (Level 1 & 2 AC Charging)

• Lithium Iron Phosphate (LFP) batteries: Set the maximum charge level to 100%. Charge to 100% at least once per month to maintain estimated in-vehicle range accuracy (both state of charge and distance to empty). If not charged to 100% at least once per month, owners may experience degraded vehicle performance and a decrease in the accuracy of the vehicle's estimated range.
• Nickel Cobalt Manganese (NCM) batteries: Set the maximum charge level to 90% to reduce strain on the battery. Setting the maximum charge level to 100% provides full range for long trips.

DC Fast Charging On-the-Road
Charging your LFP or NCM battery to 80% minimizes your time charging and reduces battery capacity degradation (since charging rates will slow between 80-100%).

https://www.ford.com/support/how-tos/electric-vehicles/home-charging/how-do-i-maintain-my-electric-vehicle-battery/#:~:text=Lithium Iron Phosphate (LFP) batteries,charge and distance to empty).

How do I know what kind of battery I have. I just got a 23 Mach E GT. I can't find the type of battery anywhere...

 

[Bilyjck]

If you have extended range battery it should be NCM. If you go to charging menu and set limits screen, if it shows 50% to 100% it is lithium.

 

[Mach1E]

Isn’t there something about regen not really working/helping when at 100% charge?

I also imagine charging near 100% is less efficient (more energy loss).

It definitely takes more time (charge rate slows as you near 100.

If these things are true it would mean it costs you more $$ to always charge to 100%.

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