From The Blackout News 

About 80 percent of the electricity needed to charge an electric car is stored in the battery, the rest is lost. How does this happen?

When a lithium-ion HV battery is discharged, lithium ions move from the cathode to the anode, generating electrical energy. When charging, the opposite happens. Here, current flows against the internal resistance of the battery, generates heat and is lost as a loss.

However, most losses occur when alternating current (AC) is converted from the grid to direct current (DC) for the high-voltage battery. On-board charging systems take over this task, and their efficiency varies between 75 and 95 percent, depending on the charging current. Losses also occur in the cables and connectors. These losses directly affect charging time and costs. 20 percent loss means 20 percent longer charging time and 20 percent higher costs.

The following values were determined by Praxis Elektroauto for 20 different models:

Car Model	Loss of charge
Kia e-Soul 39 kWh	9,8 %
Hyundai Ioniq 5 72 kWh	11,3 %
Ford Mustang Mach-e	11,3 %
Hyundai Ioniq 6 53 kWh	12,5 %
BMW i7 xDrive60	13,1 %
VW ID.3	13,4 %
Tesla Model Y Long Range	14,3 %
Mercedes EQS	14,7 %
Opel Mokka-e	15,2 %
Fiat 500 Action	16,0 %
Dacia Spring	16,7 %
BMW i4 eDrive40	17,2 %
Mazda MX-30	18,8 %
Porsche Taycan	22,0 %
Tesla Model 3	22,6 %
Mini Cooper SE	23,1 %
Polestar 2 78kWh AWD	27,0 %
Smart EQ fortwo	29,2 %
Renault Zoe Z.E. 50 E-Tech	31,1 %
Renault Twingo ZE	38,2 %

How to measure losses?

The WLTP data provides information. This globally standardized test determines the range and power consumption of electric cars. The traction battery is completely discharged and then charged with alternating current (AC). Since the energy absorbed is measured, the charging losses are included. With these values and the usable battery capacity, the losses can be calculated.

What are the charging losses in DC charging? With DC fast charging, direct current flows directly into the battery, there is no AC-DC conversion. But higher charging capacities mean more heat loss. The losses in DC charging are between 5 and 10 percent, depending on the charging power and battery system.

How to minimize charging losses?

When it comes to AC charging, the on-board charger should work efficiently, which is problematic when the current flow is low. Wallboxes and public charging stations achieve better results. The charging power should be about 90 percent of the maximum value of the on-board charger. An 11 kW on-board charger should be set to 14 amps. A short, thick charging cable also helps.