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Vehicle Battery Basics

November 22, 2013 - 1:58pm


Vehicle Battery Basics

Batteries are essential for electric drive technologies such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and all-electric vehicles (AEVs).


A battery is a device that stores chemical energy and converts it on demand into electrical energy. It carries out this process through an electrochemical reaction, which is a chemical reaction involving the transfer of electrons.

Batteries have three main parts, each of which plays a different role: the anode, cathode, and electrolyte. The anode is the "fuel" electrode (or "negative" part). The anode gives up electrons to the external circuit to create an electron flow, otherwise known as electricity. The cathode is the oxidizing electrode (the positive part). The cathode  accepts the electrons given up by the anode. The electrolyte carries the electric current as ions between the anode and cathode.

Batteries are made up of one or more basic electrochemical units called cells. Cells are usually connected in a series to increase a battery's voltage. For example, two 1.5 volt (V) AA cells connected in a series make a 3V battery.

HEVs, PHEVs, and AEVs combine batteries with controllers to create a battery system that provides energy to the vehicle. All PHEVs and AEVs can rely on the battery system alone for power, as long as the battery is sufficiently charged. Some HEVs can rely on battery power alone to drive the vehicle for short distances, while others can only use the battery system to assist the internal combustion engine.


Different batteries rely on different chemistries, depending on what they are used for. Advances in these chemistries have allowed vehicles and other applications to use larger and more powerful batteries. Most vehicles use one or more of these four major types of batteries:

  • Lead-acid batteries are the batteries most commonly used for vehicle starting and other ancillary power functions such as headlights. Lead-acid batteries can be designed to be high power, and are inexpensive and more reliable compared to other available chemistries. However, lead-acid batteries have low specific energy (energy per unit mass), perform poorly in cold temperatures, and have a shorter calendar and life cycle than other batteries chemistries when they are exposed to the same stresses.
  • Nickel-metal hydride batteries are used in a variety of applications. In particular, most currently-available HEVs use high-voltage nickel-metal hydride batteries. Although they are used fairly widely these batteries are still more expensive than lead-acid batteries.
  • Lithium-ion batteries are used in most of today's PHEVs and AEVs, as well as some HEVs. A number of consumer electronics, including mobile phones and laptops, have used lithium-ion batteries since the 1990s. Lithium-ion batteries' high specific energy, high energy efficiency, and long life make them particularly useful for these applications. The U.S. Department of Energy (DOE) and industry are working together to conduct research and development to reduce these batteries' cost, size, and weight.


Advancing battery technologies is critical as DOE works with industry to improve PHEVs and AEVs, as well as meet the EV Everywhere goal to have the U.S. become the first nation in the world to produce plug-in electric vehicles that are as affordable for the average American family as 2012's gasoline-powered vehicles by 2022. Current battery research and development investigates advanced battery chemistries such as lithium-metal, lithium-air, and lithium-sulfur. Visit the U.S. Department of Energy's Vehicle Technologies Office battery research  page for more information. 

Visit the Alternative Fuels Data Center to learn more about vehicle batteries.