Electric Vehicle Charging

Anushka Godambe
January 17, 2026

Submitted as coursework for PH240, Stanford University, Fall 2025

Introduction

Fig. 1: Electric Vehicle Recharging. (Source: Wikimedia Commons)

Electric Vehicles (EVs) are defined as cars that use electric motors for propulsion, resulting in zero tailpipe emissions (see Fig. 1). These vehicles are powered through charging systems linked to the power grid.

Types of EVs

The existing literature identifies three types of EVs described in Table 1 below, featuring Hybrid EVs (HEV), Plug-in EVs (PEV), and Fuel Cell EVs (FCEV). [1,2]

Charging Systems

While non-plug in HEVs, and FCEVs don't typically rely on charging systems, PEVs depend on grid-connected chargers which provide varied power outputs.

Level 1 chargers use 120 volts (V) of alternating current (AC) from a standard household outlet to charge an EV battery. [2] Despite the continuous power draw, the risk of power outages at home is minimal if the household electrical system is not overloaded with other high-power appliances.

Level 2 chargers use 240V of AC and can be installed in home garages, parking lots, and commercial charging stations. [1] At home, the high-power draw from Level 2 charging can stress the household electrical system if multiple appliances are used simultaneously.

Level 3 chargers use 300-800V of direct current (DC) to charge EV batteries, eliminating the need for an onboard AC to DC converter. [2] These chargers are typically found at public charging stations along highways and must be managed to prevent local spikes in electricity demand.[2]

EV Type Power Source Electricity Generation Example Vehicle Model
HEV Battery and ICE The battery stores energy from braking to power the electric motor, and the ICE generates electricity to charge the battery. Toyota Prius
PEV External Electricity Electricity is drawn from external charging systems connected to the grid and stored in a lithium-ion battery to power the electric motor. Tesla Model S
FCEV Hydrogen Electricity is generated onboard by a hydrogen fuel cell, with energy temporarily stored in a separate battery to power the electric motor Toyota Mirai
Table 1: Three-Way Comparison of Electric Vehicles. [1,2]

Extreme Fast Charging (XFC) is an extension of Level 3 that delivers up to 1000V of DC at high-power charging stations near highways and commercial areas. [2] XFC is particularly useful for large EV fleets such as buses and trucks which have higher battery capacity. [2] To support charging safety and grid stability, XFC stations incorporate advanced cooling systems to prevent overheating.

How Batteries Work in Electric Vehicles

In order to further compare the charging systems, we must first explore battery charging and discharging on an individual level. Battery charging occurs when electrical charge flows into a battery to store energy, while discharging occurs when charge flows out of a battery to power an electric vehicle.

A battery delivers power at the rate P = VI

  1. P (Power) = rate of energy delivery through the circuit (watts)

  2. V (Voltage) = energy per unit of charge (volts)

  3. I (Current) = rate of charge flow (amps)

During charging, P is supplied from the charger to the battery, and during discharging, P is delivered from the battery to the motor.

Additionally, the voltage of a battery is V = IR, according to Ohms Law.

  1. V (Voltage) = energy per unit of charge (volts)

  2. I (Current) = rate of charge flow (amps)

  3. R (Internal Resistance) = how much the circuit resists the charge flow (ohms)

During charging, voltage represents the energy per unit of charge required to push current into the battery against its internal resistance. During discharging, voltage represents the energy per unit of charge lost across the batterys internal resistance as power is delivered to the motor.

Energy lost due to internal resistance is converted to heat. By combining the equations above, we can quantify this heat generation as PL = I2 R

  1. PL (Power Loss) = rate of energy lost as heat in the circuit due to internal resistance (watts)

  2. I (Current) = rate of charge flow (amps)

  3. R (Internal Resistance) = how much the circuit resists the charge flow (ohms)

As I increases, P increases quadratically, meaning a high rate of charge flow significantly increases energy converted to heat. As R increases, P increases linearly, but since internal resistance is usually minimized for higher efficiency, most heat is generated from high currents.

Since larger batteries have a higher storage capacity, they require more energy to reach full charge. To charge a larger battery at the same speed as a smaller battery, a higher current would be needed. However, according to the power loss equation above (PL = I2R), increasing the current significantly increases energy loss as heat.

Conclusion

In conclusion, electric vehicles rely on different battery types and charging systems, with PEVs relying on grid-connected chargers. These chargers each have varying voltages and charging currents, with higher charging currents increasing power loss as heat due to internal resistance. Understanding the interaction between battery capacity, charging current, internal resistance, and resulting power loss is crucial for designing charging systems which preserve battery health as EV adoption increases.

© Anushka Godambe. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

References

[1] M. S. Mastoi et al., "An In-Depth Analysis of Electric Vehicle Charging Station Infrastructure, Policy Implications, and Future Trends," Energy Rep. 8, 11504 (2022).

[2] S. S. G. Acharige et al., "Grid Integration of Electric Vehicles - Impact Assessment and Remedial Measures," J. Power Sources 650, 236697 (2025).