Battery technology has made some drastic improvements over the past few years. We no longer feel range anxiety, as batteries are powerful enough to give us 200+ range.
However, general consumers are still confused about whether they should charge their electric vehicle battery to 100% or not.
Most manufacturers and even most experts suggest charging your battery only up to 80%.
But what is the reason? Is It Bad to Charge an Electric Vehicle to 100%?
Will the battery die soon if I charge it to 100%? Will my battery degrade over time if I charge it to 100% for a prolonged time? This article answers all these questions.
Before we find the answer to these questions, we need to understand a little bit about Lithium-Ion battery technology and how it charges, or more precisely, how it holds the charge.
How Lithium-Ion Battery Works?
Like any other battery technology, lithium-ion batteries have a positive electrode, a negative electrode, and an electrolyte. A battery pack typically contains multiple battery cells packed in an enclosure.
The positive electrode is typically made from a chemical compound called lithium-cobalt oxide (LiCoO2) or, in newer batteries, from lithium iron phosphate (LiFePO4).
The negative electrode is generally made from carbon (graphite), and the electrolyte varies from one type of battery to another.
When the battery is charging, lithium ions from the positive electrode pass through the electrolyte, go to the negative electrode, and remain there. During this process, the battery stores charges.
When the battery is discharging, lithium ions travel back to the positive electrodes, releasing energy that is used to run the vehicle’s motor.
Now the big question. Is It Bad to Charge an Electric Vehicle to 100%?
Is It Bad to Charge an Electric Vehicle to 100%?
You might notice that most manufacturers recommend charging their EV batteries up to 80%. If you look into their brochure, they mention the charging time for 0-80% charge and then about 0-100% charge.
One thing you will also notice is that a 0-80% charge is very fast, but from 80-100%, it takes a lot of time. Why is this so?
The main reason for this is that battery charging is not linear. When the battery is almost drained, ions can travel much faster, which is why the battery charges very fast from 0 to 80%.
However, beyond 80%, ions take a lot more time to travel to the negative electrode, and that is why it takes more time to charge from 80 to 100%.
Think of a cinema hall when it is empty. It is very easy to get into and find a seat. However, when the theater is almost full, it’s very difficult to find your seat.
Though a theater has nothing to do with batteries, it is a logical example that explains how a battery behaves at different states of charge.
You might feel I am okay with the extra time a battery takes to charge from 80-100%. In that case, should I charge it to 100%? Apart from the extra time, is there any issue if I charge it 100%?
Charging A Battery Up To 100% Could Be Bad
When you charge a battery up to 100%, you are simply putting a lot of stress on it because it is operating at an extreme point.
If you continue to charge 100% over time, you might notice battery degradation. It can be catastrophic, too, due to the extreme heat that the battery generates when you charge it to 100%, but that is very rare in modern batteries.
Consistently charging to 100% capacity allows the growth of lithium metal tendrils known as dendrites that can cause a short circuit.
The lithium ions fall out of circulation when caught in side reactions within the electrolyte due to the higher temperature generated from the energy stored when a battery is charged to its extreme capacity.
Occasionally charging batteries to 100% is not bad, but don’t make it a practice. Doing so will do more harm than good.
When you go on a long trip, charging a battery to 100% could be the need of the hour. That is perfectly fine.
The above graph shows that the current flow is linear in the first step up to 20% SOC; however, after that, it decreases with the increase in SOC. After 80% SOC, it takes a drastic downward flow.
So even if you charge beyond 80%, there is little current flow. That means it will take a lot of time to charge from 80% to 100%, and generally, a battery will generate the most heat during this charging period.
That is why it is better to avoid charging beyond 80%
Discharging A Battery To 0% Could Be Bad Too
Charging or discharging at extreme capacity is bad for overall battery health and longevity. The main point here is that you should not let the battery work at extreme capacity. Discharging a battery to 0% is equally bad as charging a battery to 100%.
If you want your EV batteries to be very healthy for longer and don’t want them to degrade fast, always operate at 20-80% charge.
The battery charge should not fall below 20% or above 80%. This is the best charging practice for lithium-ion batteries.
How To Stop Batteries Working At The Extreme Capacity
There are multiple ways to prevent a battery from working at extreme capacity. Most modern vehicles have an option on the dashboard to stop charging when the battery reaches 80% charge, and the same can be done when the battery reaches 20% charge.
In some cases, manufacturers do that in the battery management system. They program the BMS to show the battery State Of Charge as 100%, but in actuality, the battery charge may be only 95%. The same is true when the battery State Of Charge is 0%.
The manufacturer tries to protect the battery by automating the protection system so that it lasts longer.
However, they will usually not disclose this to consumers. That is why it is our ultimate duty not to operate an EV battery beyond the 20-80% limit.
Conclusion: Is It Bad to Charge an Electric Vehicle to 100%?
Yes, it is bad to charge an electric battery to 100%. Occasional charging is fine, but a regular practice of charging 100% could be catastrophic and damage your battery quickly.
You will soon notice battery degradation and start blaming the manufacturer without understanding that you are spoiling the battery life. So stop charging beyond 80% and stop discharging below 20%.
