If you are in the electric car community, you have probably seen that most EV companies (i.e. Nissan, Tesla, Jaguar) do not advertise the time it takes for their cars to reach a full battery. Instead, they advertise the time to charge up to 80% battery capacity. If you've ever been puzzled as to why, you're not alone.
We're here to break down why this is, how EV batteries charge, and what to actually expect from your EV battery, fast charging solutions and shorter powering sessions.
The Science Behind The Most Common Electric Vehicle Battery
Almost every electric vehicle (EV) we see out on the road today uses rechargeable lithium ion batteries. Lithium ion batteries are among the most commercially utilized for consumer electronics on the market today. They are often seen inside laptop computers, cell phones, and other personal electronic devices. They work by allowing lithium ions to move from a negative electrode to a positive electrode for discharge and back when charging.
The four key components in lithium-ion cells are the anode, the cathode, the separator, and the non-aqueous electrolyte. While you are charging up your device as normal, small lithium ions are hard at work moving from the cathode, through the electrolyte, to the anode, and ultimately return during discharge.
Why Does It Take So Long to Reach a Fully Charged EV Battery, but not 80% Capacity?
Modern Battery Electric Vehicles (BEV) can achieve most of their charge in under an hour using a Level 3 fast charger. However, it takes disproportionately longer to power up that last 20 percent of battery capacity.
Due to voltage and individual battery limits, charging a BEV slows down considerably after the battery has reached 80% capacity. Most lithium batteries, including those used for electric cars, have a nominal voltage of 3.7 volts per cell.
As an individual battery cell’s charge voltage gets closer to 4.2, which usually happens after 80% battery capacity, the current flowing to the battery must be reduced to ensure that you don't exceed the limit.
The Bottom Line
The rate of charging must be reduced at around 80% capacity to avoid any major problems, and onboard charging system in each BEV thereby slows down your charge time in order to best protect your battery.
This is why the last 20 percent of a battery’s charge capacity always takes so much longer to achieve, and why automakers advertise charging rates based on the capacity which utilizes the nominal voltage per cell. If companies were to advertise the time to reach a full charge, the promised quotes to customers would be far less impressive.
With this in mind for EV customers, it is often easier to think about the miles added rather than the battery capacity percentage reached in shorter charging sessions. Most Level 3 fast chargers can add 125+ miles to your range in as little as 25-30 minutes or 250+ miles in an hour—despite not reaching a 100% charge for likely several hours after that.
Charging clients should expect commercial Level 3 chargers to come in handy and deliver results should they need a fast charge. However, it is important for all daily EV drivers to understand that driving away from a fast charging session with a battery charged to 80% is the norm and what is most often recommended by the car manufacturer as well as the fast charging device.
The home/work level 2 charger plays a pivotal role in the health of your battery, as these devices can help safely charge your car's battery from 80% to 100% over the course of a few hours, so unless you are planning a longer trip, 80% capacity should be plenty to work with for daily commuting.